"-"^"f^llsS'iassfiir' 


^^^^^IZ  '^^  "metallic  inlay. 

RECAP 


:t 


HW 


'yoo 


B,  S.  U,  L^  S,  :\ 


jtMM  — OUaHiTni  Mif  a 


LI  N 


/ 


*::>  V^f:iJ^-^ii^s. 


CoHege  of  ^tjpsiiciang  anb  burgeons! 


%ihvavv 


<^V^^t<^ 


METALLIC  INLAY. 


BY 


ZAHNARZT  H.  W.  C.  BODECKER,  B.8.,D.D.S.,M.D. 


WITH  158  ILLUSTRATIONS 
AND  14  PLATES. 


BERLIN: 
HERMANN  MEUSSER. 

STEGLITZERSTR.  58. 

1911. 


Copyright  1911  by  Hermann  Meusser,  Berlin. 


Druck  der  Spamerschen  Buchdruckerei  in  Leipzig. 


To  My  Father, 

C.  F.  W.  Bodecker,  d.d.s.,  m  d.s  , 


This  Book  Is 
Affectionately  Dedicated. 


Digitized  by  tine  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/metallicinlayOObd 


Introduction. 

The  metallic  inlay,  and  with  it  the  general  application  of 
casting,  is  undoubtedly  one  of  the  most  valuable  acquisitions 
made  by  dentistry  in  the  last  few  years.  As  a  result  of  its 
success  in  practice,  the  gold  inlay  has  become  a  recognized 
means  of  filling  teeth.  The  fact  that  metallic  inlays  are 
indicated  only  in  the  posterior  teeth,  does  not  detract  from 
their  value,  as  in  this  position,  the  inlay  is  superior  to  all 
other  classes  of  fillings. 

The  value  of  the  inlay  process  was  recognized  many  years 
ago;  the  material  and  the  method  of  constructing  the  inlay 
itself,  offered  difficulties  however.  To  the  ingenuity  of  Tag- 
gart,  in  America,  and  of  Solbrig,  in  Europe  the  dental  pro- 
fession is  indebted  for  a  metallic  inlay  which  fulfills  all  just 
requirements. 

The  object  of  this  book  is  to  explain  in  a  concise  manner, 
the  mechanical  principles  upon  which  the  retention  of  metalhc 
inlays  depends;  to  apply  these  principles  to  the  preparation 
of  cavities,  and  to  formulate  a  method  of  procedure  in 
making  and  setting  inlays.  Though  intended  primarily  as 
a  practical  guide,  theoretical  considerations  could  not  be 
disregarded,  as  it  is  never  wise  to  make  a  single  step  in  any 
practical  operation  without  knowing  the  theoretical  reason. 

In  writing  this  book  the  arrangement  of  the  German 
edition  has  been  followed.  It  has  been  revised  in  some  points, 
and  a  chapter  on  inlay  abutments  has  been  added. 

The  technique  suggested,  can  by  no  means  be  considered 
complete.  It  is  offered,  so  that  others  may  improve  upon  it. 
If  this  little  book  in  any  way,  directly  or  indirectly,  should 
help  in  furthering  the  progress  of  the  metallic  inlay,  the 
work  of  the  writer  will  not  have  been  in  vain. 


Contents. 


Introduction. 

Index  of  Plates.  page 

Chapter        I.    The  Evolution  of  the  Metallic  Inlay 1 

Chapter       II.    The  Advantages  and  Disadvantages  of  the   Metallic   Inlaj'  5 

Chapter     III.    Retention  of  Metallic  Inlays 16 

Cement-Retention 17 

Self-Retention 26 

Chapter     IV.    Retention  and  Cavity  Form 35 

Chapter       V.    Caries  and  Cavity  Form 53 

Chapter     VI.    The  Enamel  Margin 62 

Chapter    VII.    Instruments  for  Cavity  Preparation 68 

Chapter  VIIJ.    Cavity  Preparation 74 

Chapter     IX.    The  Impression 90 

The  Indirect  Impression 90 

The  Direct  Impression      92 

The  Hollow  Wax  Model 102 

Chapter       X.    The  Construction  of  the  Inlay 104 

By  Older  Methods 104 

By  Casting 107 

The  Investment 107 

The  Casting  Metal 112 

The  Casting  Macliines 118 

Combination  Inlays 127 

Chapter     XI.    Setting  the  Inlay 131 

Fitting  the  Inlay 131 

The  Cement 139 

Drying  the  Cavity 142 

Setting  the  Inlay 144 

Finishing  and  Polishing 145 

Chapter  XII.    The  Inlay  as  a  Bridge  Abutment      148 

Index 165 


Index  of  Plates. 


Plate         I.    Lower  Molar  with  Mesio-Occlusal  Cavity 76 

Plate       II.    Lower    Molar  with  Disto-Proximal  Cavity.      Adjoining  Tooth 

Missing      77 

Plate     III.    Lower  Molar  mth  Lingual  Wall  Missing 78 

Plate      IV.    Lower  Molar  with  Abraded  Occlusal  Surface      . 79 

Plate        V.    Lower  Bicuspid  in  a  Crowded  Arch,  with  Mesio-Occlusal  Cavity  80 
Plate      VI.    Upper  Bicuspid  ^^ith  Large  Mesial  and  distal  Cavities  (Tooth 

Pulpless) 81 

Plate    VII.    Upper  Bicuspid  Aiith  Lingual  Wall  Missing .  82 

Plate  VIII.    Upper  Bicuspid  with  Buccal  Wall  Missing 82 

Plate     IX.    Upper  Bicuspid  with  Erosion      84 

Upper  Bicuspid  mth  Simple  Cervical  Cavity 84 

Plate       X.    Cuspid  with  Small  Distal  Cavity 85 

Plate     XL    Cuspid  with  Large  Distal  Cavity 86 

Plate    XII.    Abraded  Cuspid,  A-^ith  Inlay  Anchored  on  the  Lingual  Surface  87 

Incisor  with  Small  Proximal  Cavity      87 

Plate  XIII.    Incisor  with  Mesial  and  Distal  Cavities        88 

Plate  XIV.    Abraded  Incisor  \\ith  Mesial  and  Distal  Cavities       89 


Chapter  I. 
The  Evolution  of  the  Metallic  Inlay. 

Never  will  it  be  known  to  whom  the  honor  belongs  of 
having  placed  the  first  gold  inlay  in  a  tooth.  Those  who  long 
ago  practiced  this  method,  kept  their  discovery  a  dark  secret. 
Even  the  patient  was  not  informed  that  the  "gold  filling" 
inserted,  differed  in  any  way  from  one  made  in  the  usual 
manner.  Now,  however,  that  the  gold  inlay  has  become  a 
recognized  means  of  filling  teeth,  the  long  guarded  secret  of 
the  first  gold  inlays  transpires.  In  all  cases,  the  "method" 
was  about  the  same.  A  large,  imperfectly  prepared  cavity 
was  laboriously  filled  with  gold,  the  matrix  removed  and  the 
filling  polished.  Before  the  finishing  was  completed,  however, 
the  whole  filling  had  loosened.  After  some  hesitation,  the 
operator  determined  to  reset  the  filling  with  cement,  and  at 
a  subsequent  sitting  to  polish  the  filling,  —  if  possible,  or,  if 
necessary,  —  confess.  If  success  attended  the  experiment,  the 
filling  was  finished  and  booked  in  the  journal  with  a  question- 
mark.  In  how  many  cases  this  mark  was  justified  will  never 
be  ascertained.  There  are,  however,  cases  on  record  where  such 
fillings  have  performed  effective  service  for  five,  ten,  and  even 
fifteen  years,  as  proven  by  patients  presented  at  dental  con- 
ventions. 

I  mention  these  cases  only,  to  call  attention  to  the  fact 
that  we  have  to-day  examples  which  prove  that  the  gold 
inlay  can  favorably  compare  in  durability  with  the  foil  filling. 
But  not  only  upon  the  inlays  produced  as  the  result  of  an 
accident,  is  our  experience  based,  but  also  upon  intentio- 
nally constructed  inlays  that  were  inserted  many  years 
ago.  Since  that  time,  a  great  number  of  methods  for  inlay 
construction  have  been  proposed,  but,  especially  in  the  be- 
ginning, a  lack  of  interest  prevented  the  profession  at  large 

Bodecker,  Metallic  Inlay.  1 


from  adopting  the  inlay  process.  Tlie  introduction  of  por- 
celain as  a  filling  material,  however,  resulted  in  the  recognition 
of  the  advantages  of  the  inlay.  This  material,  extensively 
used  for  several  years  in  all  classes  of  cavities,  is  now  limited 
to  visible  cavities  in  the  anterior  part  of  the  month.  During 
the  porcelain  era  a  certain  number  of  men  did  not  loose 
faith  in  the  gold  inlay.  They  experimented  and  perfected  their 
methods,  until  the  profession  in  general,  dissappointed  at  the 
failure  of  porcelain  in  the  posterior  teeth,  was  willing  to  give 
the  gold  inlay  a  fair  trial.  The  rapidity  with  which  this  method 
of  filling  has  won  new  adherents  in  the  last  few  years,  is  due 
less  to  the  failure  of  porcelain,  than  to  the  increased  simplicity 
in  the  production  of  the  metallic  inlay. 

One  of  the  oldest  methods,  in  imitation  of  the  inlays 
accidentally  made,  as  described  above,  consisted  in  lightly 
filling  the  cavity  with  sponge-gold,  carefully  removing  the 
whole,  saturating  with  solder  and  resetting  with  cement. 
Numerous  other  methods  soon  followed,  in  which  a  matrix, 
as  used  for  glass  and  porcelain  inlays,  played  the  most  im- 
portant part.  The  difference  in  these  methods  lay  in  the  use 
of  various  kinds  of  foil,  viz.,  gold,  gold  and  platinum,  and 
pure  platinum;  in  the  method  of  removing  the  matrix  from 
the  cavity;  and  in  the  use  of  gold  of  different  karats  for  filling 
the  matrix  and  for  the  production  of  contours  and  cusps. 

The  success  attending  the  use  of  gold  inlays  in  large  cavities 
justified  the  attempt  to  use  them  for  still  larger  restorations. 
The  difficulty  of  building  up  such  large  contours  and  cusps 
with  sponge-gold  and  solder,  soon  brought  forth  new  methods. 
A  matrix  was  made  of  thin  24  kar.  plate.  A  cap,  suitable 
for  the  case,  was  swedged  on  the  die  plate  of  a  crown  outfit 
and  the  requisite  part  soldered  upon  the  matrix.  In  this 
manner  the  first  hollow  inlay  originated.  This  procedure  was 
soon  improved  upon  in  so  many  ways,  that  the  hollow  gold 
inlay  can  claim  more  methods  for  its  construction  than  any 
other  inlay  filling,  be  it  of  gold  or  porcelain.  In  spite  of  these 
numerous  methods,  the  construction  of  hollow  inlays,  instead 
of  becoming  simpler,   became   more   and  more   complicated. 

In  the  meantime  the  solid  gold  inlay  had  made  progress. 


The  matrix,  upon  a  model  of  the  cavity,  was  filled  with  wax, 
tried  in  the  mouth,  replaced  on  the  model,  and  the  essential 
surfaces,  that  is,  grinding  surface  and  contactpoint,  were 
smoothly  covered  with  foil.  The  whole  was  then  invested, 
leaving  only  the  uncovered  wax  exposed.  The  latter  was 
burned  out  and  the  resultant  chamber  filled  with  molten  gold 
or  solder.  The  next  step  was  to  neglect  the  foil  covering,  and 
to  completely  embed  the  matrix  with  its  wax  form.  To  pro- 
duce a  channel  to  the  surface,  a  pin  around  which  a  cone  of 
wax  had  been  formed  was  stuck  into  the  wax  model.  A  vent 
was  produced  by  a  straw  running  from  the  model  to  the 
surface.  The  investment  was  then  heated  until  the  wax 
burned  out.  In  a  small  depression  beside  the  opening  of  the 
channel,  the  gold  was  melted  with  a  blow-pipe.  At  the  proper 
moment  the  mold  was  tipped,  so  that  the  gold  flowed  into 
the  channel  and  into  the  mold.  In  this  manner,  as  suggested 
by  Solbrig  (Paris),  the  first  cast  gold  inlay,  made  by  the  wax 
dispersion  method,  was  produced.  To  simplify  the  process, 
an  electric  furnace  was  constructed.  It  consisted  of  tw^o  parts; 
a  lower,  which  could  be  heated  to  600 — 700  °F,  for  the 
reception  of  the  mold,  and  an  upper  part  in  which  the  gold 
was  fused.  By  removing  a  plug,  the  gold  flowed  down  into 
the  mold. 

The  finer  details  of  the  wax  model  could  not,  however, 
be  reproduced  without  pressure.  In  the  methods  of  casting 
employed  in  the  arts,  this  is  obtained  by  using  a  large  amount 
of  excess  metal.  As  this  is  not  practicable  in  casting  gold, 
it  was  necessary  to  devise  other  means  of  obtaining  sufficient 
pressure. 

Dr.  W.  IT.  Taggart  solved  the  difficulty,  and  in  doing  so 
inaugurated  a  new  era  in  dentistry.  Not  alone  was  the  con- 
struction of  perfect  inlays  made  possible,  but  also  in  crown 
and  bridge-work,  as  well  as  in  plate-work,  has  the  value  of 
casting  become  evident.  The  writer  fully  agrees  with  the 
words  spoken  by  Solbrig  at  the  Dental  Congress  held  in 
Lille,  1909*.    "In  these  various  methods  the  construction  of 


*)  Ash's  Quartely  Circular,  Jan.   1910. 


a  matrix  in  gold  or  platinum  was  still  indispensable,  and  it 
was  Taggart,  of  Chicago,  who  first  did  away  with  it,  by  the 
application  of  pneumatic  pressure  in  combination  with  the 
wax  dispersion  method.  His  merit  lies  not  only  in  the  in- 
genious invention  of  his  apparatus,  but  also,  and  above  all, 
in  the  influence  which  he  exercised  upon  many  colleagues  with 
inventive  minds,  who  were  led  by  his  enthusiasm  and  his 
success  to  make  research  in  the  same  direction.  Before  his 
apparatus  could  be  procured  several  other  systems  were  pressed 
upon  the  notice  of  the  profession,  but  not  withstanding  this 
Dr.  Taggart  must  without  doubt  be  considered  the  pioneer 
of  the  present  period,  as  regards  the  casting  of  metals." 


Chapter  II. 

The  Advantages   and  Disadvantages   of   the  Metallic 

Inlay  Filling. 

The  interest  which  the  dental  profession  has  shown  for  the 
gold  inlay  during  the  past  few  years,  proves  that  this  method 
of  filling  teeth  has  steadily  been  gaining  general  recognition. 
The  enthusiasts,  however,  go  decidedly  too  far  in  claiming  the 
method  to  be  everywhere  applicable.  They  recall  the  porcelain 
fanatic,  who  in  answer  to  the  question  "Where  is  porcelain 
indicated  ?"  replied,  "On  the  hundred  and  sixty  surfaces  of 
the  thirty  two  human  teeth."  Experience,  sad  to  say,  has 
taught  us  something  different.  Those  who  to-day  predict  that 
in  the  near  future  mallet,  plugger,  and  gold  foil  will  become 
relics  of  the  past,  may  wait  a  long  time  for  the  fulfillment  of 
their  prophecy. 

The  truth  of  Franklin's  motto :  "A  place  for  everything,  and 
everything  in  its  place,"  has  been  amply  demonstrated  by  the 
filling  materials  introduced  into  dentistry  in  the  past.  I  need 
only  recall  the  fact  that  cement,  amalgam  and  later  porcelain, 
each  at  first  indiscriminately  used,  are  to-day  confined  to 
certain  definite  spheres  of  usefulness.  That  the  metallic  inlay 
will  prove  an  exception  to  this  rule,  may  be  doubted,  in  spite 
of  the  many  good  qualities  that  this  form  of  filling  possesses. 

The  disadvantages  of  the  above  filling- materials  are  well 
known.  Cement  is  more  or  less  rapidly  dissolved  under  the 
mechanical  and  chemical  influences  in  the  mouth.  Amalgan 
often  presents  an  unesthetic  appearance,  is  liable  to  change 
its  form,  and  under  certain  circumstances  discolors  the  tooth. 
Porcelain,  on  account  of  the  nature  of  the  material,  cannot 
be  burnished  against  the  margins  of  the  cavity,  and  a  seam, 
equal  in  width  to  the  thickness  of  the  foil  used  for  the  matrix, 
must  therefore  always  remain.   This  seam  constitutes  the  chief 


disadvantage  of  the  porcelain  inlay.  When  in  time  the  cement 
is  dissolved  at  this  point,  the  edges  of  the  inlay  being  un- 
supported, chip  off;  they  then  become  rough  and  often  dis- 
colored. The  ideal  result,  a  restoration  true  to  nature,  is  not 
attained  under  such  circumstances. 

The  gold  inlay  is  free  from  the  imperfections  mentioned 
in  connection  with  the  above  filling- materials,  but  its  con- 
struction requires  a  high  degree  of  accuracy  in  order  to  pro- 
duce a  perfect  filling.  This  fact  has,  by  some,  been  considered 
a  deficiency  of  the  metallic  inlay  system.  The  success  or 
failure  of  an  inlay  is  determined  by  its  adaptation  to  the 
cavity  margin.  The  durability  of  an  inlay  is  absolutely  assured, 
if  the  space  between  the  edge  of  the  inlay  and  the  enamel 
margin,  is  limited  to  the  theoretical  thickness  of  thinly- mixed 
cement.  The  possibility  of  producing  such  inlays  has  been 
demonstrated,  but  it  is  not  probable  that  even  the  majority 
of  gold  inlays  show  such  perfection  at  all  their  margins.  Every 
operator  should  however  remember,  that  in  placing  an  im- 
perfectly adapted  gold  inlay  into  a  tooth,  he  is  not  only  doing 
himself  and  his  patient  an  injustice,  but  that  he  is  also  in- 
juring the  repute  of  a  valuable  filling-method,  to-day  on  trial 
before  the  dental  profession. 

Before  discussing  the  question  of  advantages,  disadvantages, 
and  general  indications  for  the  use  of  the  metallic  inlay,  atten- 
tion must  be  called  to  the  functions  of  the  cement.    These  are : 

1.  to  intimately  unite  the  inlay  with  the  tooth; 

2.  to  fill  out  all  space  between  the  inlay  and  the  cavity  wall. 
The  contention  that  in  the  same  manner  as  the  impression 

was  removed  from  the  cavity,  the  inlay  itself  may  drop  out 
if  the  cement  does  not  happen  to  be  sufficiently  adherent, 
rests  upon  a  misinterpretation  of  facts.  Without  here  entering 
into  a  discussion  of  this  subject  (see  Chap.  Ill)  it  must  be 
mentioned,  that  a  truly  adherent  cement  is  not  necessary. 
With  almost  any  cement  on  the  market,  a  metallic  inlay  can 
be  firmly  set  in  the  cavity.  Adhesion  plays  no  essential  part, 
as  the  attachment  depends  upon  entirely  different  mechanical 
principles.  The  quality  most  desirable  in  a  cement  for  this 
purpose    is   resistance   to    compression   strain,    i.  e.    crushing 


strength.  In  order  to  utilize  this  property,  the  undercuts  in 
the  inlay  and  in  the  tooth  must  be  in  such  relative  position, 
that  the  inlay  cannot  be  removed  from  the  cavity  without 
crushing  the  layer  of  cement.  The  shape  of  a  properly  formed 
inlay,  materially  aids  the  cement  in  preventing  a  displace- 
ment of  the  inlay.  The  topic  of  self-retention  will  be  dis- 
cussed in  Chapter  III. 

The  second  function  of  the  cement,  the  filling  out  of  all 
spaces  between  the  inlay  and  the  cavity  wall,  has  always  been 
the  point  of  attack  of  those  opposed  to  all  systems  of  inlays. 
To  simplify  the  discussion  of  this  question,  it  has  been  divided 
into  two  parts. 

1.  The  office  of  the  cement  in  the  depth  of  the  cavity, 
i.  e.,  between  dentine  and  inlay,  and 

2.  The  office  of  the  cement  at  the  margin  of  the  cavity, 
i.  e.,  between  enamel  and  inlay. 

The  cement  layer  in  the  depth  of  the  cavity  should  be  as 
thick  as  possible.  Especially  is  this  necessary  in  large  cavities 
in  teeth  with  living  pulps,  in  order  to  interpose  a  layer  of 
thermally  non-conducting  material  between  the  large  mass  of 
metal  and  the  pulp.  Besides  this,  a  thick  layer  of  cement  is 
more  advantageous  in  holding  the  inlay  in  the  cavity. 

It  has  been  claimed  by  the  opponents  of  inlay  fillings, 
that  thinly  mixed  cement  cannot  be  considered  a  reliable 
filling  material.  As  proof,  they  cite  the  disintegrated  and 
evil-smelling  cement  sometimes  found  upon  the  removal  of 
shell  crowns  that  have  been  worn  a  long  time.  As  proof  to 
the  contrary,  mention  may  be  made  of  the  cement  layer  found 
upon  the  walls  of  those  cavities  out  of  which  porcelain  inlays 
have  fallen.  The  hardness  and  density  of  the  cement  in  such 
places  leaves  nothing  to  be  desired.  If  putrefaction  occurs, 
it  denotes  the  presence  of  organic  matter  in  the  cement.  This 
is  possible  only  under  two  conditions.  Either  the  cement  is 
so  porous  that  it  can  easily  be  permeated  by  the  organic 
constituents  of  the  saliva,  or  an  admixture  of  saliva  has  taken 
place  at  the  time  when  the  crown  was  being  set  into  place. 
The  latter  is  by  far  the  more  reasonable  assumption. 

Besides  mechanically  filling  out  all  spaces,  the  cement  has 


been  proven  to  have  a  physiological  action  on  the  dentine. 
No  other  filling-material  is  capable  of  producing  such  marked 
changes  through  which  the  dentine  becomes  considerably  more 
resistant  to  caries.  The  investigations  of  C.  F.  W.  Bodecker 
upon  the  reaction  of  the  dentine  under  various  filling-materials, 
have  amply  proven  this  fact.*)  Under  oxyphosphate  of  zinc 
"the  reaction  is  almost  constantly  present,  and  consists  of 
a  solidification  of  the  dentine  and  an  obliteration  of  a  number 
of  dentinal  canaliculi.  The  dentinal  canaliculi  which  are 
obliterated  under  oxyphosphate  fillings  first  become  faint, 
scarcely  traceable  and  ultimately  disappear,  in  consequence 
of  which  disappearance  the  fields  of  basis-substance  between 
the  dentinal  canaliculi  are  considerably  broadened  .  .  .  The 
consolidation  is  densest  along  the  border  of  the  cavity,  where 
dentinal  canaliculi  are  quite  scanty;  but  the  consolidated 
dentine  extends  to  a  considerable  depth  before  it  blends  with 
normal  dentine"  (Fig.  1). 

Upon  the  reaction  of  the  dentine  under  gold  fillings,  the 
same  author  expresses  himself  as  follows :  "In  some  instances  no 
reaction  was  noticeable  in  the  dentine,  only  a  zone  of  green  co- 
lour, attributable  to  causes  just  mentioned  under  gutta-percha." 
(Due  to  coagulants  applied  before  the  introduction  of  the 
filling.)  "In  other  instances  there  was  a  distinct  reaction  along 
the  border  ...  In  still  other  instances  the  goldfilling  has 
led  to  a  partial  obliteration  of  dentinal  canaliculi  similar  to 
that  induced  by  oxyphosphate  of  zinc,  though  never  as  com- 
plete as  that  which  follows  the  introduction  of  the  last-named 
filling-material."  Under  amalgam  and  under  tin  the  reaction 
of  the  dentine  is  similar  to  that  under  gold.  From  these  observa- 
tions the  great  value  of  cement  as  a  filling- material  becomes 
apparent.  It  changes  normal  dentine,  which  is  easily  destroyed 
by  caries,  into  a  tissue  which  has  the  appearance  and  the  re- 
sistance of  so-called  senile  dentine.  This  is  probably  the  reason 
why  secondary  decay  hardly  ever  appears  at  the  margin  of 
a  cavity  filled  with  an  inlay. 

Opponents  of  the  gold  inlay  have  recently  asserted,  that 
as  these  observations  were  made  in  cases  of  teeth  filled  with 

*)  C.  F.  W.  Bodecker,    Anatomy   and  Pathology  of  the  Teeth,  page  323. 


porcelain,  the  assumption  that  metallic  inlays  will  show  the 
same  immunity  to  secondary  caries  is  not  justifiable.  They 
believe  in  the  possibility  of  an  electric  circuit  being  set  up 
between  the  gold  and  the  zinc  of  the  cement,  with  the  result, 
that  conditions  favorable  for  the  beginning  of  caries  would 


^   hi'!/! 

// 

' 

V  / 

lii  ////- 

/ 

/    /    / 

-■    /   ' 

///^ 

Fig.   1. 


be  produced.  There  is,  however,  no  evidence  in  support  of 
this  theory,  and  it  may  be  safely  assumed  that  owing  to  the 
reaction  of  the  dentine  under  the  cement,  secondary  caries 
will  be  observed  as  rarely  under  a  metallic  inlay  as  it  has 
been  under  porcelain. 

In  setting  an  inlay,  more  or  less  pressure  is  always  exerted 
upon  the  thin  cement.  Whether  this  is  sufficient  to  force  the 
cement  into  the  dentinal  canaliculi  and  interglobular  spaces. 


10 

and  whether  the  reaction  of  the  dentine  is  more  marked  than 
under  an  ordinary  cement  fiUing,  are  questions  that  cannot 
at  present  be  answered,  as  the  experiments  conducted  by  the 
writer  are  not  as  yet  complete. 

The  subject  most  important  in  all  inlay  methods  will  now 
be  considered,  i.  e.  the  cement  seam  between  the  inlay  and  the 
margin  of  the  cavity.  Theoretically  the  width  of  the  narrowest 
possible  seam  is  equal  to  a  single  layer  cement  grains.  The 
production  of  such  a  seam  is  possible  only  in  certain  places 
and  under  the  most  favorable  circumstances.  In  discussing 
this  question  it  will  be  assumed  that  the  width  of  the  seam 
is  such  as  occurs  with  a  well-fitting  inlay,  constructed  accord- 
ing to  the  methods  now  in  vogue.  As  in  every  other  class  of 
filling,  the  durability  of  an  inlay  depends  upon  the  accuracy 
of  its  adaptation  to  the  cavity  margin.  If  therefore,  an  inlay, 
imperfect  in  this  respect,  is  set  into  a  tooth,  its  permanency 
is  doubtful  from  the  beginning.  For  the  failure  of  such  a 
filling,  the  inlay-process  cannot  be  held  accountable. 

The  durability  of  the  cement  is  dependent  upon  the 
position  of  the  seam  on  the  surface  of  the  tooth.  Either  it 
lies  on,  or  near,  the  grinding-surface,  where  it  is  exposed  to  the 
pumping  action  of  mastication,  as  it  is  named  by  C.  J.  Grieves*), 
or  it  lies  toward  the  neck  of  the  tooth,  unaffected  by  this 
action.  The  conditions  in  the  latter  position  will  be  dis- 
cussed first. 

In  spite  of  claims  to  the  contrary,  cement,  in  time,  dissolves 
more  or  less  in  almost  every  month.  Exceptions  to  this  rule 
are  so  rare  that  they  may  completely  disregarded.  This  fact 
would  apparently  justify  the  assumption  that  the  cement 
within  the  seam  would  in  time  be  completely  dissolved  out. 
An  examination  of  a  large  number  of  seams  in  positions  un- 
affected by  the  pumping  action  of  mastication  has,  however, 
proven,  that  the  cement  is  only  dissolved  out  to  a  depth  equal 
to  the  width  of  the  seam,.  This  rule,  it  must  be  mentioned,  does 
not  hold  good  for  seams  exposed  to  the  action  of  mastication. 

The  explanation  of  this  fact,  so  important  for  the  durability 


*)  Dental  Summary.     Vol.  27,  p.  93. 


n 

of  the  inlay,  rests,  according  to  C.  J.  Grieves  and  others,  upon 
the  protective  action  of  the  mucus  present  in  the  secretions 
of  the  mouth.  All  surfaces  in  the  mouth,  with  the  exception 
of  those  cleansed  by  mastication,  are  normally  covered  by 
a  layer  of  mucus.  W.  D.  Miller  described  mucin  as  a  clear,  vis- 
cous fluid,  of  alkaline  reaction.  It  is  albuminous,  and  there- 
fore forms  a  nutrient  medium  for  bacteria.  It  mixes  with  water, 
in  the  form  of  threads,  without  being  soluble.  It  is  insoluble 
in  alcohol,  ether,  chloroform,  and  dilute  acids ;  soluble  in  dilute 
alkalies  and  in  concentrated  acids.  The  layer  of  mucus  on 
the  teeth,  containing  albuminous  bodies,  offers  the  putrifac- 
tive  bacteria  of  the  mouth  a  suitable  medium.  As  the  reaction 
during  putrifaction,  at  least  in  the  first  stages,  is  alway  alka- 
line, the  decomposition  of  mucus  cannot  act  as  a  factor  in 
the  causation  of  caries. 

The  protective  action  of  the  mucus  on  the  cement  is 
explained  by  the  fact,  that  mucin  is  insoluble  in  water  and 
in  dilute  acids.  As  soon  as  the  cement  is  dissolved  out  of  a 
seam  so  far,  that  the  mucus  layer  is  no  longer  destroyed  by 
the  circulation  of  fluids  during  mastication,  or  in  cleansing 
the  teeth,  the  solution  of  the  cement  ceases.  This,  as  has 
been  already  mentioned,  occurs  when  the  solution  has  pro- 
ceeded to  a  depth  equal  to  the  width  of  the  seam. 

Some  interesting  investigations  have  been  made  upon  this 
subject  by  J.  Head*).  He  found  that  a  seam  filled  with 
Harvard  Cement,  and  placed  in  a  one  percent,  watery  solution 
of  lactic  acid,  dissolved  out  in  two  to  three  days.  The  same 
material  under  the  same  circumstances,  placed  in  a  one  percent 
solution  of  lactic  acid  in  saliva,  showed  no  evidence  of  being 
attacked.  Head,  also,  believes  this  to  be  due  to  the  presence 
of  the  mucin  in  the  saliva. 

If  the  seam  lies  on  the  occlusal  surface,  the  above  men- 
tioned rule  does  not  apply,  because  the  pumping  action  of 
mastication,  as  well  as  the  mechanical  contact  of  the  food, 
prevents  the  formation  of  a  sufficiently  thick  layer  of  mucus. 
This  evil,  the  most  dangerous  of  all,  for  the  inlay  process, 


*)  Dental  Cosmos  Vol.  XLVII,  p.  789. 


12 

has  been  the  subject  of  much  thought,  and  many  experiments. 
It  is  evident  that  in  this  position  the  width  of  the  seam  must 
be  confined  to  its  theoretical  minimum.  The  narrower  the 
seam,  the  less  disturbance  can  be  caused  by  the  pumping- 
action,  and  the  stronger  is  the  action  of  the  capillary  attraction 
holding  the  mucus  layer  in  place. 

To  make  such  seams  less  vulnerable,  bevelling  the  cavity 
margin  has  been  suggested.  The  success  of  this  measure  alone 
may  be  doubted,  as  the  seam  remains  exposed  to  the  pumping 
action.  The  author  beleives  that  the  only  possible  protection 
against  the  solution  of  the  cement  in  this  place,  is  an  almost 
theoretically  perfect  adaptation  of  the  inlay  to  the  cavity 
margin. 

For  this  reason  the  author  adheres  to  the  use  of  24  kar. 
gold  in  the  construction  of  inlays.  With  this  material  it  is 
easy,  especially  on  the  occlusal  surface,  to  force  the  gold 
against  the  margin  of  the  cavity  with  a  tomato-burnisher. 
The  disadvantages  of  24  kar.  gold  are :  that  high  cusps  cannot 
be  built  up  in  case  of  a  sharp  bite;  that  it  does  not  take  as 
smooth  a  polish  as  22  kar. ;  and  that  considerably  higher  heat 
is  necessary  in  casting.  The  objection,  that  an  inlay  of  24  kar. 
gold  is  much  softer  than  a  hammered  foil  filling,  does  not  affect 
its  usefulness.  If  a  pure  gold  inlay,  which  is  a  trifle  too  high, 
is  examined  in  the  mouth,  it  will  show  that  the  area  con- 
stantly struck  by  the  antagonist,  is  harder  than  any  foil  filling. 

The  time  necessary  for  the  construction  of  an  inlay  has, 
by  some,  been  considered  as  an  objection  to  inlay  methods. 
If,  however,  the  inlay  is  used  only  where  large  surfaces,  con- 
tours, or  cusps  are  to  be  restored,  this  process  offers  a  decided 
saving  of  time. 

Another  apparently  more  justifiable  objection  is,  that  all 
inlays  require  an  extensive  sacrifice  of  healthy  tooth- structure. 
If  by  this  is  meant  a  thorough  cutting  out  of  the  fissures, 
then  it  can  only  be  of  advantage  in  protecting  the  tooth  from 
redecay.  If  it  refers  to  the  ruthless  destruction  of  tissue, 
simply  to  make  the  removal  of  the  impression  easy,  or  to 
produce  a  typical  box-shaped  cavity  with  steps  and  squared 
angles,  then  the  objection  is  more  than  justified.    An  inlay 


r.', 

cannot  be  made  in  quite  such  narrow  limits  as  an  amalgam, 
(jr  an  ordinary  gold  filling.  But  if  we  compare  the  cavity- 
preparation  of  a  conservative  inlay  operator,  with  a  cavity 
prepared  according  to  the  teachings  of  Black,  but  little  diffe- 
rence in  the  extent  of  the  cavities  will  be  found.  In  some 
cases  it  will  even  be  in  favor  of  the  inlay  (see  Chap.  V). 

The  advantages  the  tooth  derives  from  the  use  of  the  inlay 
are  briefly  as  follows: 

1.  The  cement  causes  a  reaction  in  the  dentine,  making 
it  more  resistant  to  decay. 

2.  The  cement  forms  an  insulating  layer,  which  protects 
to  pulp  from  rapid  changes  of  temperature. 

3.  The  cement,  intimately  uniting  the  inlay  with  the  tooth, 
gives  support  to  weakened  vzalls. 

4.  The  cement  adheres  to  dry  dentine,  so  that  in  the  case 
of  self-retentive  inlays,  under  cuts,  if  properly  placed, 
need  not  be  very  deep  at  excessively  sensitive  places. 

5.  Very  weak  walls  which  are  liable  to  fail  later  may  be 
removed,  as  the  work  of  constructing  an  inlay  does  not 
depend  upon  its  size. 

6.  Prolonged  malleting,  which  often  causes  a  hyperaemia 
of  the  pulp  or  a  slight  pericementitis,  is  avoided. 

7.  The  danger  of  fracturing  a  wall,  due  to  the  expansion 
of  the  filling  under  the  mallet,  as  well  as, 

8.  The  danger  of  injuring  the  enamel  margin  with  a  plugger, 
cannot  occur  with  an  inlay. 

9.  Contours  and  contact-points  of  inlays  are  more  easily 
built  up,  and  preserved  while  finishing,  than  those  of 
fillings  made  in  the  mouth. 

10.  Cusps  with  proper  articulation  can  be  readily  produced 
on  an  inlay. 

11.  The  filling  is  of  a  uniform  density.  Hollow  spaces  are 
not  present,  and  the  surface  is  smooth.  An  exfoliation, 
as  is  often  the  case  with  foil  fillings,  does  not  take  place ; 
food  particles,  etc.  can  therefore  not  adhere. 

12.  Over  porcelain,  the  metallic  inlay  has  the  advantage, 
that  the  seam  is  not  increased  in  width  by  the  removal 
of  the  matrix. 


14 

13.  The  use  of  the  metallic  inlay  enables  us  to  fill  cavities 
with  gold,  which  on  account  of  their  unfavorable  position, 
cannot  be  filled  with  a  foil  filling.  For  example,  cervical 
cavities  extending  deeply  under  the  gum,  where  the  use 
of  the  dam  is  not  possible. 

14.  Many  extensively  decayed  teeth,  upon  which  shell- 
crowns  are  usually  set,  may  do  good  service  for  years, 
if  restored  by  means  of  a  metallic  inlay. 

For  the  patient  also,  the  inlay  process  offers  conveniences 
which  he  soon  learns  to  appreciate. 

1.  The  time  consumed  by  the  work  in  the  mouth  is  con- 
siderably shortened. 

2.  The  use  of  the  mallet,  the  rubberdam  and  its  accompany- 
ing evils,  the  ligature  and  the  clamp,  are  avoided. 

3.  Separators  are  applied  less  often. 

4.  Setting  an  inlay  takes  no  longer  than  introducing  an 
ordinary  cement  filling. 

5.  The  operation  of  filling  a  tooth  with  an  inlay,  may  be 
discontinued  at  more  stages  than  with  other  fillings. 

Besides  being  more  agreeable  to  the  patient,  the  inlay  pro- 
cess offers  certain  advantages  to  the  operator.  In  case  of  large 
fillings,  a  saving  of  time  is  effected.  But  the  chief  value  is, 
that  the  operator,  knowing  to  a  certainty  whether  the  filling 
he  has  placed  into  a  tooth  is  perfect  or  not,  can  foretell  its 
durability  more  positively  than  if  he  had  used  any  other  filling 
material. 

The  indications  for  the  use  of  metallic  inlays  are  briefly 
the  following: 

1.  In  all  larger  cavities  where  a  sufficiently  direct  and  free 
access  for  the  introduction  of  a  foil  filling  cannot  be 
obtained.  Such  are  the  cavities  on  the  distal  surfaces 
of  the  bicuspids  and  molars.  In  cases  of  extensive  decay, 
the  inlay  may  also  be  used  on  the  mesial  surface  of 
these  teeth. 

2.  Large  defects  of  the  grinding  surface,  requiring  a  restora- 
tion of  the  cusps. 

3.  In  all  cervical  cavities  extending  beneath  the  gum  in 
the  molars,  and,  exceptionally,  in  the  bicuspids. 


15 

4.  To  make  large  restorations  on  the  teeth  of  children  and 
nervous  patients. 

5.  In  cases  of  so  called  soft  teeth,  where  secondary  caries 
usually  appears  at  the  margin  of  the  most  carefully 
introduced  metallic  fillings. 

6.  In  building  up  abraded  cutting  edges  of  the  incisors 
and  cuspids. 

7.  In  teeth  loosened  from  any  cause. 

8.  Teeth  loosened  by  pyorrhea  may  be  supported  by  solder- 
ing together  a  series  of  proximal  inlays  at  their  con- 
tact points. 

9.  Interproximal  spaces  into  which  the  food  easily  packs, 
may  be  restored  to  normal  conditions,  by  inserting 
inlays  with  exaggerated  contours. 

10.  As  bridge  abuttments,  various  inlays  have  been  sug- 
gested and  some  successfully  used. 

11.  In  orthodontia,  inlays  alone  or  in  connection  with  an 
apparatus  may  occasionally  be  used  to  retain  the  teeth. 

12.  In  making  shell  crowns,  the  true  bite  may  be  obtained, 
by  modelling  wax  onto  the  band  in  the  mouth,  invest- 
ing, and  casting  the  occlusal  surface  directly  onto  the 
band. 

In  spite  of  the  number  of  indications  mentioned  above, 
it  is  to  be  doubted  whether  the  result  would  be  a  success  in 
every  case.  The  chief  disadvantage  of  the  inlay  process,  the 
difficulty  of  producing  perfect  adaptation  at  the  cavity  margin, 
would  justify  the  assumption  that  it  is  almost  impossible  to 
solder  a  number  of  inlays  together  without  endangering  their 
perfect  adaptation  to  the  margin  of  the  cavity.  As  a  filling 
method,  however,  the  metallic  inlay  process  deserves  full 
recognition,  if  its  application  be  limited  to  filling  larger  cavities 
of  the  bicuspids  and  molars. 


Chapter  III. 
Retention  of  Metallic  Inlays. 

The  durabihty  of  an  inlay  is  largely  dependent  upon  its 
mode  of  attachment  to  the  tooth.  In  porcelain  inlays  the 
chief  reliance  was  placed  upon  the  adhesive  qualities  of  the 
cement.  In  the  case  of  the  metallic  inlay,  however,  the  cavity 
may  be  so  prepared  that  the  inlay  receives  support  in  every 
direction  except  in  that,  opposite  to  the  one  in  which  it  was 
inserted  into  the  cavity.  If  this  direction  is  parallel  to  that 
of  the  pressure  of  mastication,  the  inlay  cannot  be  bitten  out 
of  the  cavity  as  long  as  the  tooth  remains  intact.  The  possi- 
bility of  giving  the  cavities  such  a  favorable  form  is  due  to 
the  fact  that  metal,  in  contradistinction  to  porcelain,  is  suffi- 
ciently resistant  to  the  force  of  mastication,  to  permit  the 
construction  of  comparatively  thin  anchorage-extensions,  fit- 
ting snugly  into  the  fissures  and  grooves  of  the  tooth. 

The  retention  of  the  finished  inlay  should  be  considered 
in  the  early  stages  of  cavity-preparation.  Before  beginning 
with  the  excavation  of  the  dentine,  the  direction  and  amount 
of  the  force  of  mastication  must  be  studied,  and  the  position 
determined,  where  sufficient  anchorage  may  be  obtained  on 
the  tooth.  Which  form  of  anchorage  should  be  chosen  in  a 
given  case,  depends  upon  the  position  and  the  depth  of  the 
cavity,  upon  the  structure  of  the  tooth  itself,  and  upon  the 
distribution  of  the  healthy  tissue  about  the  cavity. 

The  writer  has  divided  the  retention  of  inlays  into  two 
classes : 

1.  Retention    depending    upon    an    intermediary    body. 
(Cement-retention.) 

2.  Retention  depending  upon  the  form  of  the  inlay  itself. 
(Self -retention.) 


17 
Cement-Retention. 

Retention  Depending  upon  an  Intermediary  Body. 

The  material  used  for  the  attachment  of  metallic  inlays 
is  oxyphosphate  of  zinc  cement.  Sufficient  data  has  been 
gathered  during  its  use  in  connection  with  porcelain  inlays,  to 
prove  that  this  material  possesses  the  necessary  qualities  for 
setting  metallic  inlays.  The  fact  that  thinly  mixed  cement 
adheres  to  dentine  is  generally  recognized,  but  the  explanations 
regarding  it  differ.  It  has  been  claimed,  that  a  chemical  union 
takes  place.  A  more  probable  explanation  is  that  the  acid, 
corroding  the  dentine,  produces  a  rough  surface  on  which 
the  cement  obtains  a  purely  mechanical  hold.  However  this 
may  be,  the  cement  is  sufficiently  adherent  to  the  dentine 
for  the  purpose  of  retaining  the  inlay  in  a  cavity.  The  hold 
which  the  cement  finds  on  the  surface  of  the  inlay  is  purely 
mechanical,  and  should  be  the  subject  of  special  attention. 
This  hold  may  be  produced  in  two  ways,  either  by  deeply 
undercutting  with  a  saw  or  knife-edged  stone,  or  by  roughening 
with  a  pointed  instrument.  Which  of  these  two  methods  is 
to  be  used  in  a  given  case,  depends  on  the  following  circum- 
stances. If  the  free  surface  of  the  inlay  is  comparatively 
larger  than  that  within  the  cavity;  or  if  the  inlay  is  exposed 
to  the  force  of  mastication  without  itself  having  sufficient 
self-retention ;  or  if  the  cement  layer  between  inlay  and  cavity- 
wall  is  very  thin,  deep  undercuts  are  to  be  used.  A  general 
roughening  of  the  surface,  being  easier  to  produce  than  the 
undercuts,  is  indicated  where  the  latter  are  deemed  unneces- 
sary. 

The  Undercut. 

If  deep  undercuts  are  to  be  made  use  of,  they  should  be 
so  placed  that  those  in  the  inlay  lie  exactly  opposite  to  those 
in  the  walls  of  the  cavity  (Fig.  2).  The  retention  of  the  inlay 
is  dependent  in  this  case,  upon  a  ring  of  cement  whose  strength 
is  proportional  to  the  compression-strength  of  the  cement,  and 
to  the  thickness  of  the  ring.  If  the  undercuts  in  the  inlay 
and  in  the  tooth  are  exactly  opposite  each  other,  the  force 
necessary  to  dislodge  the  inlay  is  equal  to  that  which  could 

Bii decker,  Metallic  Inlay.  2 


18 

crush  a  layer  of  the  thickness  a—h  (Fig.  3  A)  of  the  cement 
used  to  set  the  inlay.  If  the  undercuts  are  not  quite  opposite 
one   another,    the  effective  thickness  of  the  ring  is  reduced 


Fig.  2. 


to  G — d  (Fig.  3  B).  In  case  no  parts  of  the  undercuts  face 
each  other,  they  become  practically  useless.  The  cement  lying 
in  the  undercut  in  the  tooth  (II,  Fig.  3  C)  finds  little  or  no  hold 


A 


Fig.  3. 


on  the  inlay.  This  undercut  is  therefore  superfluous.  Owing 
to  the  fact  that  thinly-mixed  cement  adheres  to  dentine,  the 
cement  in  the  undercut  in  the  inlay  (I,  Fig.  3  C),  finds  some 
hold  on  the  cavity  wall.  The  retention  so  obtained  is,  however. 


19 


not  comparable  to  that  of  a  ring  of  cement,  or  that  produced 
by  a  general  roughening  of  the  surface  of  the  inlay. 

As   experience  has  shown  the  difficulty  of  bringing  the 
undercuts  in  exact  apposition,  a  more  certain  method  of  trans- 


Fitr.  4. 


mitting  the  pressure  from  the  inlay  to  the  tooth  is  required. 
By  thickening  the  layer  of  cement  between  the  inlay  and 
the  cavity  walls  at  certain  points,  a  more  uniform  distribution 
of  pressure  is  obtained.     This  is  accomplished  by  a  further 


Fis.  5. 


excavation  of  the  walls  of  the  cavity;  this  in  most  cases 
obviates  the  necessity  of  making  undercuts  in  the  tooth  (Fig.  4). 
In  a  cavity  such  as  Fig.  5,  a  deep  undercut  at  a,  would 
appreciably  weaken  the  edge  b.  A  slight  excavation,  as 
shown,  would  be  equally  effective  in  anchoring  the  inlay.  It 
may   be  stated  here  as  a  general  rule,   that  undercuts  with 


20 

square  angles  (Fig.  9  B  and  C)  alway  weaken  a  structure  more 
than  if  these  angles  were  rounded  (Fig.  10). 

All  undercuts  made  into  an  inlay  must  be  of  proper  form 
and  in  their  theoretically  correct  position.  To  understand  this 
correct  form  and  position,  the  part  played  by  the  cement  in 
the  retention  of  an  inlay  must  be  studied.  Its  chief  function 
will  be  made  clear  by  the  following:  Two  metal  parts  with 
holes  drilled  at  a  and  h,  are  suspended  as  shown  in  Fig.  6. 


Fig.  6. 

If  a  and  h  were  filled  with  exactly  fitting  metallic  rods  it  would 
be  almost  impossible  to  separate  the  parts.  If  the  holes  were 
filled  with  cement,  plaster,  sealing-wax,  or  rosin,  the  weight 
necessary  to  separate  the  parts  would  vary  with  each  sub- 
stance. 

The  moment  that  the  separation  of  the  parts  begins, 
a  change  of  form  of  the  holes  a  and  b  takes  place  (Fig.  7). 
If  the  holes  are  filled,  the  filling  must  bear  the  weight  of  the 
whole  mass  placed  on  the  scale-tray  below.  The  diameter  of 
the  hole,  a — h  (Fig.  8  a),  tends  to  diminish,  and  pressure  is 
therefore  exerted  upon  the  filling  material  in  the  direction  a — b. 
At  the  same  time  the  diameter  c — d  elongates,  so  that  the 


21 

filling  material  looses  its  support  in  this  direction.  As  long 
as  the  filling-material  possesses  sufficient  resistance  to  com- 
pression, i.  e.  crushing  strength,  to  prevent  a  change  of  form 
of  its  mass,  no  movement  of  the  parts  can  take  place.  The 
value  of  a  material  for  this  purpose  is  therefore  dependent 
upon  its  crushing  strength. 

The  pressure  which  a  material  can  bear  is  dependent  upon 
the  area  subjected  to  pressure,  as  well  as  upon  the  thickness 
of  the  material  itself.  These  facts  must  be  taken  into  con- 
sideration in  determining  the  form  and  position  of  an  undercut. 


Fig.  7. 


Fig.  8  a. 


In  selecting  the  position,  leverage  by  which  the  inlay  might 
be  pried  out  of  the  cavity  during  mastication,  must  be  taken 
into  account.  As  the  margin  of  the  cavity  acts  as  a  fulcrum, 
it  is  evident  that  the  farther  the  undercut  (hold)  is  away 
from  the  margin  of  the  cavity,  the  greater  will  be  the  force 
necessary  to  dislodge  the  inlay.  For  this  reason,  undercuts 
are  to  be  placed  near  the  floor  in  simple  cavities. 

The  difficulty  of  bringing  the  undercuts  in  the  tooth  and 
in  the  inlay  in  apposition  has  already  been  mentioned.  By 
changing  the  form  of  the  undercuts  and  widening  the  cavity 
in  certain  places,  a  more  favorable  distribution  of  pressure  in 
the  cement  layer  can  be  brought  about.  Fig.  9 — 12  are  en- 
largements of  the  shaded  portion  of  Fig.  8  b.   Fig.  9  shoves  the 


22 

wall  of  a  cavity  slightly  enlarged  at  A,  and  having  an  under- 
cut made  with  a  wheel  at  B.  The  inlay  is  undercut  with 
a  saw  at  C.  If  an  attempt  is  made  to  remove  the  inlay  in  the 
direction  of  the  arrow,  pressure  will  be  set  up  in  the  cement 
layer.  The  main  pressure  between  inlay  and  tooth  will  be 
born  by  a  cone  of  cement,  of  the  form,  ahcd. 

The  resistance  which  the  cement  offers,  depends  mainly 
upon  the  direction  of  the  pressure  cone  a — d  in  relation  to 
the  direction  in  which  the  inlay  may  be  removed  from  the 
cavity.  The  more  nearly  these  two  directions  correspond,  the 
more  does  the  cement  depend  upon  its  crushing  strength  for 
the  retention  of  the  inlay.    Another  factor  determining  the 


Fig.   8  b. 


effective  resistance  of  the  cement,  is  the  area  of  the  cross- 
section  of  the  pressure  cone.  Other  things  being  equal,  the 
larger  the  area,  the  stronger  the  retention. 

A  consideration  of  Fig.  9,  will  show,  that  the  undercuts  C 
and  B  could  have  been  made  less  deep,  without  thereby  de- 
creasing the  sectional  area  of  the  pressure  cone;  that  is,  the 
inlay  would  have  been  equally  resistant,  if  the  undercuts  were 
of  the  form  a,  h,  c  and  e,  d,  c.  It  also  becomes  apparent,  that 
if  the  corner  e  were  removed,  the  pressure  cone  would  gain 
in  cross-sectional  area,  and  at  the  same  time  lie  in  a  con- 
siderably more  favorable  direction.  The  cement  in  the  depths 
of  the  undercuts  C  and  B  takes  little  or  no  part  in  the  retention 
of  the  inlay.  Fig.  10  shows  the  undercuts,  correct  in  form  and 
position;  the  points  discussed  in  Fig.  9  having  been  practi- 
cally applied.  The  corner  e  (Fig.  9)  has  been  removed,  and 
the  pressure  cone,  now  filling  out  the  entire  space,  has  thereby 
been  widened  and  brought  into  a  more  favorable  direction. 


21} 

The  undercuts  are  less  deep,  and  have  no  sharp  angles.  The 
latter  is,  however,  of  less  importance  with  metaUic  than  with 
porcelain  inlays.  The  form  of  undercut  in  the  tooth.  Fig.  10, 
weakens  the  wall  far  less  than  one  made  with  a  wheel.  The 
lower  part  of  the  undercut  in  the  inlay,  has  been  cut  obliquely 
so  that  the  pressure  cone  rests  at  right-angles  upon  the  sur- 
face of  the  inlay. 

A  further  advantage  of  this  form  of  undercut  is  the  follow- 
ing.   It  is  a  known  fact  that  most  cements  expand  while 


///////////////y/,-y//^'.'  '^///.'///^//y//  '/^//X 


Fig.  9. 


Fig.   10. 


setting.*)  This  causes  the  inlays,  set  with  such  cements,  to 
rise  out  of  the  cavity  to  a  greater  or  lesser  extent.  If,  however, 
undercuts,  correct  in  form  and  in  relative  position  be  used 
(Fig.  10),  an  expansion  of  the  cement  does  not  force  the 
inlay  out,  but  on  the  contrary,  presses  it  more  firmly  into  the 
cavity.  In  such  cases  attention  should  be  paid  to  the  fact, 
that  the  mass  of  the  cement  mu.t  be  contained  in  the  under- 
cuts, the  cement  at  all  other  points  being  limited  to  the 
thinnest  possible  layer. 


*)   See  Poundstone"s  table  p.  140. 


24 

Where  the  undercut  in  the  inlay  lies  above  that  in  the 
tooth  (Fig.  11),  the  pressure-cone  finds  but  little  hold  upon 
the  almost  vertical  wall  of  the  cavity.  The  retention  of  the^ 
inlay  in  this  case  does  not  depend  upon  the  crushing  strength, 
but  almost  v/hoUy  on  the  tensile  strength  of  the  cement. 
Tension,  like  compression,  spreads  through  a  mass  in  the  form 
of  a  cone.  Therefore,  in  the  cement  layer  of  Fig.  11a  tension- 
cone  will  extend  from  the  undercut  a — h  in  the  direction  c. 


'  "'itlll  III!  "Illll  III  III' 


Ym.    11. 


Fig.   12. 


The  cross-sectional  area  at  a  is  too  small  to  give  sufficient 
retention  to  the  inlay.  As  the  tensile  strength  of  cement  is 
far  lower  than  its  compression,  or  crushing  strength,  the 
sectional  area  of  the  tension-cone  must  be  far  greater  than 
that  of  the  pressure-cone  to  give  the  same  retention.  Besides 
this,  it  is  necessary  to  make  regular  undercuts  in  the  tooth 
as  well  as  the  inlay,  as  the  adhesive  qualities  alone  can  not 
be  depended  upon  (Fig.  12). 

Roughening  the  Surface. 

The  second  method  of  producing  a  hold  for  the  cement 
is  by  roughening  the  under  surface  of  the  inlay  with  a  sharp 
instrument.    Hersey*)  recommends  the  Bonwill  mallet.    Any 


G.  S.  Hersey,  Dental  Cosmos,  Nov.  1906,  p.  1167. 


mechanical  mallet  with  a  sufficiently  strong  blow  can  be  used. 
The  writer  has  had  the  best  and  quickest  results  by  using 
a  sharp  instrument  in  the  mechanical  engraving  instrument, 
shown  in  Fig.  113. 

If  the  cement  layer  is  thin,  the  blows  must  fall  at  right- 
angles  to  the  surface,  so  that  the  roughening  consists  of  in- 
numerable depressions  placed  close  to  one  another.  An  en- 
largement of  one  of  these  depressions  is  shown  in  Fig.  13. 
Where  the  cavity  has  been  widened,  the  point  of  the  instrument 
is  applied  obliquely  to  to  surface,  and  small  step-like  pro- 
jections are  thrown  up  (Fig.  14).    The  projections  should  be 


Fig.  13.  Fig.   14 


miniature  reproductions  of  the  undercut  shown  in  Fig.  10. 
The  step  should  always  face  the  direction  in  which  the  inlay 
can  be  removed  from  the  cavity,  so  that  the  retention  may 
depend  upon  the  crushing  strength  of  the  cement.  A  slight 
widening  of  the  cavity,  below  the  margin,  is  the  only  treat- 
ment the  tooth  requires  before  setting  the  roughened  inlay. 
Regular  undercuts  into  the  dentine  are  unnecessary. 

The  retention  of  a  roughened  inlay  depends  upon  the 
number  and  size  of  the  pressure-cones  produced  by  the  pro- 
jections. These  in  turn  are  dependent  upon  the  area  of  the 
surface  of  the  inlay  within  the  cavity.  A  roughening  is  there- 
fore indicated  in  proximal,  cervical,  and  labial  inlays,  as  they 
are  not  exposed  to  mastication  and  their  free  surface  is  always 
less  than  that  within  the  cavity.  Proximal  inlays  in  molars 
and  bicuspids  may  be  roughened  if  they  are  sufficiently  an- 


26 

chored  by  means  of  self-retention.  Regular  undercuts  are, 
however,  to  be  used  in  the  restoration  of  incisive  edges,  corners, 
and  cusps. 

Upon  what  might  be  called  accidental  retention,  rests  the 
explanation  of  the  durability  of  so  many  inlays,  gold  as  well 
as  porcelain,  that  have  been  set  in  improperly  prepared  cavi- 
ties. Upon  the  dentine  the  cement  always  finds  sufficient 
hold.  On  the  inlay  there  are  usually  present,  in  smaller  or 
greater  numbers,  projections  accidentally  formed.  If  some  of 
these  are  favorably  placed,  the  cement  finds  a  support  to 
resist  compression.  The  strength  of  such  retention  is  very 
small,  and  being  a  matter  of  chance,  should  be  totally  dis- 
regarded. 

Ketention  by  means  of  cement  may  always  be  depended 
upon  if  employed  only  in  cases  where  it  is  indicated.  The 
preparation  of  the  cavity  must  be  correct,  and  there  should 
be  a  mechanical  reason  for  the  position  of  each  undercut. 
The  practice  of  indiscriminately  under-cutting  both  tooth  and 
inlay  is  unscientific,  and  is  probably  the  cause  of  .many 
failures. 

Self-Retention. 

Retention  Depending  upon  the  Form  of  the  Inlay  Itself. 

Inlays  of  this  description  are  confined  almost  exclusively 
to  the  molars  and  bicuspids.  The  hold,  or  anchorage  of  a 
self-retentive  inlay  must  be  so  located,  that,  without  depend- 
ing upon  the  retentive  power  of  the  cement,  it  can  easily 
resist  the  forces  which  tend  to  dislodge  the  inlay  during 
mastication.  The  extent  of  the  hold,  which  the  inlay  finds 
upon  the  tooth,  is  of  less  importance  than  its  location.  A  slight 
hold  at  the  proper  place,  is  more  valuable  than  a  stronger  an- 
chorage at  a  point  where  it  can  not  counteract  the  forces 
which  tend  to  dislodge  the  inlay.  Though  all  so-called  self- 
retentive  inlays  do  not  strictly  fulfill  the  above  requirements, 
they  nevertheless  are  anchored  in  more  directions  than  inlays 
depending  entirely  upon  cement-retention. 

The  strength  and  the  direction  of  the  force  acting  upon 
an  inlay,  are  dependent  upon  the  size  and  form  of  the  occlusal 


surface.  The  direction  of  the  force  is  of  prime  importance. 
If  the  antagonist  strikes  the  obHque  occlusal  surface  of  the 
inlay  (Fig.  15),  force  will  be  exerted  in  two  directions;  toward 
the  middle,  and  toward  the  neck  of  the  tooth.  The  more 
oblique  the  surface,  the  greater  will  be  the  pressure  forcing 


Fig.   15. 


the  inlay  into  the  cavity.  This  fact  is  of  practical  significance 
if  two  adjoining  proximal  cavities  are  to  be  filled  with  inlays. 
As  in  this  case  the  position  of  the  contact  points  is  not  pre- 
determined, they  may  be  placed  slightly  nearer  the  cervical 
margin  than  normally,  thereby  giving  the  inlay  a  decidedly 
more   oblique   occlusal  surface   (Fig.  16).     Such  a  procedure 


Fig.   16. 

is  valuable  in  filling  bicuspids  extensively  destroyed  by  caries, 
as  it  obviates  the  necessity  of  cutting  deeply  into  the  weakened 
walls  in  order  to  obtain  complete  anchorage  by  this  means 
alone. 

If  the  occlusal  surface  is  horizontal,  as  in  the  case  of  the 
molars,  simply  closing  the  jaws  will  force  the  inlay  against 
the  cervical  margin,  while  the  masticatory  movements  will 
tend  to  tip  the  inlay  out  of  the  cavity.  To  prevent  such 
dislocations,  the  inlay  must  be  formed  so  that  it  finds  a  hold 


upon  the  tooth.  In  order  to  determine  the  exact  location  of 
this  hold  or  anchorage,  the  different  phases  during  the  dis- 
location of  an  inlay  must  be  understood.  The  inlay  may  be 
dislodged  in  two  ways,  depending  upon  the  shape  of  the  cavity. 
If  the  wall  at  the  cervical  margin  is  narrow  (Fig.  17),  the 
inlay  is  insufficiently  supported  against  vertical  pressure.    It 


Fig.   17. 


Fig.   U 


may  then  be  forced  out  of  the  cavity,  as  on  an  inclined  plane, 
and  the  margin  a  at  the  same  time  fractured.  In  the  second 
case,  where  the  wall  is  wide  enough  to  give  support  against 
the  vertical  pressure,  forces  acting  obliquely  produce  a  leverage 
which  tends  to  tip  the  inlay  out  of  the  cavity  (Fig.  18).    The 


Fig.   19. 


Fio-.  20. 


cervical  margin  always  acts  as  the  fulcrum.  To  successfully 
oppose  this  leverage,  is  the  function  of  a  self-retentive  inlay. 
To  a  limited  extent,  porcelain  inlays  of  this  description 
have  been  made.  In  Stockholm,  in  1902,  N.  S.  Jenkins  showed 
such  a  porcelain  inlay  made  by  Ottolengui  (New  York).  The 
inlay  (Fig.  19)  was  compact,  without  thin  processes  or  ex- 
tensions. On  account  of  the  brittleness  of  porcelain  this  was 
the  only  form  possible  for  a  self-retentive  inlay  made  of  this 
material.  Though  this  cavity  form  (Fig.  20)  was  very  ingenious, 
it  was  not  applicable  to  larger  cavities,  as  in  such  cases  suffi- 


2U 

cient  tooth-substance  was  lacking.  The  difficulty  of  preparing 
such  cavities  has  caused  this  form  to  be  discarded.  For  metal 
inlays  other  forms,  more  satisfactory  and  easily  made,  have 
been  adopted. 

Metal,  in  contradistinction  to  porcelain,  not  being  brittle, 
permits  the  construction  of  thin  processes  and  extensions 
which  firmly  anchor  the  inlay  into  the  tooth. 

Groove  Anchorage. 

In  considering  the  action  of  the  leverage  shown  in  Fig.  18, 
it  becomes  apparent,  that  the  dislocation  is  greatest  at  a, 
and  gradually  decreases  toward  the  point  b.     If  this  fact  is 


Fig.  21. 


Fig.  2-2. 


practically  applied,  an  inlay  of  the  form  shown  in  Fig.  21 
will  result.  The  extension  is  strongest  at  a.  This,  the  point 
of  greatest  movement  during  dislocation,  is  farthest  away  from 
the  fulcrum,  and  is  also  most  easily  accessible  in  cutting  the 
groove  into  the  cavity  wall.  The  extension  need  not  be  carried 
to  the  point  h  as  sufficient  anchorage  can  be  obtained  at  a, 
to  firmly  lock  the  inlay  in  the  cavity  (Fig.  22). 

Fissure  Anchorage. 

If  the  lateral  walls  of  a  proximal  cavity  are  weak  or  entirely 
absent,  or  if  the  fissures  in  the  occlusal  surface  require  filling, 


Fig.  23. 


30 

the  anchorage  mentioned  above  should  not  be  used.  In  such 
cases  the  fissure-anchorage  is  indicated.  The  fissure  is  excavated 
until  a  fissure  running  in  a  bucco-lingual  direction  is  reached 
(Fig.  23).  This  is  excavated  in  one  or  both  directions.  If  a 
fissure  of  this  description  is  not  present  an  artificial  one 
running  in  this  direction  must  be  made. 

Hook-Anchorage. 

This  form  of  anchorage  is  indicated  in  cases  where  the 
occlusal  surface  has  been  almost  entirely  destroyed  (Fig.  24), 


Fig.  24. 


and  where  at  the  same  time  the  lingual  or  buccal  wall  is 
lacking.  With  a  thin  disk-wheel  a  groove  is  cut  into  the 
occlusal  surface  of  the  remaining  wall.  At  its  outer  end  the 
groove  is  extended  vertically  for  a  short  distance  [a,  Fig.  25). 


Fiff.  25. 


Fig.  26. 


The  resultant  inlay  then  has  a  hooklike  process,  which  pre- 
vents any  dislocation  through  the  forces  of  mastication.  If  two 
opposing  walls  are  standing,  the  double  hook-retention  not 
alone  anchors  the  inlay,  but  it  also  gives  support  to  weakened 
walls  (Fig.  26).  This  form  of  anchorage  is  of  value  in  pulpless 
molars,  where  the  proximal  surfaces  have  been  extensively 
destroyed  by  caries,  and  the  weakened  buccal  and  labial  walls 
still  remain  standing. 


31 


Dove-tail  Anchorage. 


This  is  a  modification  of  the  form  just  described.  Strength 
is  the  first  requisite  of  the  wall  into  which  such  an  anchorage 
is  placed.  The  dove-tail  cavity  should  have  walls  {a  and  b. 
Fig.  27)  parallel  to  the  direction  in  which  the  inlay  may  be 


Fig.  27. 

removed  from  the  cavity.  The  floor  of  the  cavity  (a,  Fig.  28) 
should  incline,  from  within  outward,  toward  the  neck  of  the 
tooth.  The  segment  c  (Fig.  27)  of  the  inlay  should  be  suffi- 
ciently strong  to  prevent  stretching  of  the  metal  at  this  point, 
under  the  force  of  mastication.  If  the  body  of  the  inlay  is 
firmly  seated  (Fig.  28),  thereby  resisting  all  vertical  pressure. 


Fig-.  28. 


the  segment  c  need  not  be  excessively  strong.  If,  however, 
the  floor  of  the  main  cavity  is  narrow  or  sloping,  the  segment 
must  resist  the  vertical  as  well  as  the  oblique  forces  of  masti- 
cation, and  must  therefore  be  accordingly  strong.  The  pre- 
paration for  the  dove-tail  anchorage  is  made  with  a  knife- 
edged  stone,  and  the  resultant  inequalities  in  the  floor  finished 
with  a  thin  wheel.  For  larger  inlays,  this  is  the  most  easily 
and  quickly  made  form  of  anchorage ;  a  strong  wall  is,  however, 
always  necessary. 


32 

Anchorage  through  Combination  of  two  Cavities. 

Inlays  having  this  form  of  anchorage  are  used  in  filling 
molars,    and   more    often   bicuspids,    v/ith    cavities    on   both 


Fig.  29. 

mesial  and  distal  surfaces  (Fig.  29).  The  same  applies  to 
inlays  extending  over  the  cutting  edges,  of  the  incisors  and 
cuspids. 

Reciprocal  Anchorage  of  two  Inlays. 

If  one  or  both  of  the  proximal  cavities  in  a  molar  or  bicus- 
pid extend  to  the  neck  of  the  tooth,  it  is  preferable  to  obtain 
retention  by  means  of  reciprocal  anchorage  of  two  inlays.  This 
method  has  several  advantages.    As  two  impressions  are  taken. 


Fig.   30. 

each  may  be  removed  in  the  direction  most  convenient.  If  a 
single  impression  of  both  cavities  were  to  be  taken,  much 
healthy  tooth  structure  would,  in  most  cases,  have  to  be 
sacrificed  in  order  to  allow  the  impression  to  draw.  Another 
point  is  the  difficulty  of  making  a  perfect  inlay  which  in- 
volves three  surfaces  of  a  tooth. 

The  procedure  of  combining  two  inlays  is  as  follows  (Fig.  30). 


33 


An  impression  is  taken  of  the  more  difficult  cavity.  The 
inlay  I,  should  not  extend  to  the  occlusal  surface.  At  b,  a 
depression  should  be  made,  and  the  surface  sloped  in  the 
direction  a.  This  is  done  upon  the  wax-model.  The  inlay  is 
then  completed  and  set  into  the  cavity  and  an  impression 
of  the  remaining  part  of  the  cavity  taken.  The  second  inlay  II, 
Fig.  30,  is  made  and  set  in  the  usual  manner.  By  means  of 
the  projection  c,  and  the  inclined  surface  a,  the  second  inlay 
anchors  the  first  in  the  tooth.  The  second  inlay  is  itself  an- 
chored by  the  projection  and  the  inclined  plane  as  well  as 
by  the  hold  it  finds  on  the  walls  of  the  fissures  and  in  the 
second  cavity. 

Pin -Anchorage. 

Another  form  of  retention  which  may  be  used  in  double 
as  well  as  single  inlays,  is  the  pin-anchorage.    At  the  proper 


Fig.  31. 


point,  a  canal  is  drilled  through  the  inlay  into  the  one  lying 
beneath,  and  into  this  a  pin  of  suitable  size  is  set  with  cement. 


Fig.  32. 


For  double  inlays  the  projection  described  above  is  preferable, 
as  it  is  easer  to  construct  and  does  the  same  service.  This 
form  of  anchorage  may,  however,  be  used  where  other  methods 


Bodecker,  Metallic  Inlay. 


34 

are  not  easily  applicable,  as  in  restoring  the  corners  of  in- 
cisors (Fig,  31).  In  certain  forms  of  inlay  bridge -abutments 
this  method  of  anchorage  has  been  employed.  The  principal 
use  of  the  pin-anchorange  is  in  restoring  the  abraded  sur- 
faces of  molars  and  bicuspids.  The  pins  are  let  into  the  tooth, 
and  removed  with  the  impression.  The  inlay  is  then  cast 
onto  the  pins  (Fig.  32).  In  the  experience  of  the  writer, 
German-silver  has  proved  to  be  the  best  material  for  such 
pins.  In  casting,  the  gold  forms  a  perfect  union  with  this 
metal. 


Chapter  IV. 
Retention  and  Cavity-Form. 


The  practical  apphcation  of  the  different  forms  of  an- 
chorage will  be  discussed  in  a  later  chapter.  The  fundamental 
principles  of  retention,  which  must  be  considered  in  the  pre- 
paration of  every  cavity,  should  be  perfectly  well  understood 
by  those  doing  inlay  work. 

The  cavity  for  an  inlay  should  be  so  prepared,  that  the 
wax  model  or  the  impression  may  be  removed  without  dis- 
tortion, and  that  the  inlay  may  find  sufficient  hold  on  the 
tooth  to  resist  the  force  of  mastication.  This  hold  should, 
whenever  possible,  depend  upon  the  shape  of  the  inlay,  and 


Fig.  33. 


not  upon  an  intermediary  binding-material,  such  as  cement. 
In  complex  cavities  this  requirement  is  easily  fulfilled.  In 
simple  cavities  the  conditions  are,  however,  somewhat  different. 
When  porcelain  inlays  were  first  introduced,  many  opera- 
tors, gave  the  cavities  a  saucer-shaped  form,  assuming  that 
the  adhesion  of  the  cement  would  keep  the  inlay  in  position. 
Numerous  failures  occured;  but  these  were  ascribed  to  in- 
equalities in  the  adhesiveness  of  the  cement.  A  consideration 
of  Fig.  33  will  show  that  the  position  of  the  undercuts  in  a 
saucer-shaped  cavity  are  most  unfavorable  for  cement-reten- 
tion. The  walls  of  the  cavity,  and  therefore  also  the  sides 
of  the  inlay,  lie  obliquely  to  the  direction  in  which  the  inlay 


36 

may  be  removed  from  the  cavity.  (Fig.  34.  An  enlargement 
of  an  undercut  in  Fig.  33.)  The  undercuts  in  the  inlay  are 
placed  above  those  in  the  tooth;  a  condition  which  has  been 
described  in  discussing  Fig.  11  and  12.  The  retention  of  the 
inlay  is  therefore  entirely  dependent  upon  the  tensile  strength 
of  the  cement.  This  is  probably  a  truer  explanation  of  the 
failures  than  the  assumption  of  differences  in  the  adhesive 
qualities  of  the  cement. 

To  avoid  these  failures,  it  was  then  suggested  to  prepare 
the  cavity  in  the  shape  of  a  box,  and  to  confine  the  thickness 


Fia-.   34. 


of  the  cement  layer  to  a  minimum.  This  procedure  undoubtedly 
gave  the  inlay  a  sort  of  self-retention.  The  box-shape  was 
then  adapted  to  other  cavities.  By  far  the  greater  majority 
of  the  authors  writing  upon  the  subject  of  cavity  preparation 
for  gold  inlays,  have  recommended  the  box-shape,  strictly 
carried  out,  for  complex  cavities  in  molars  and  bicuspids. 
This  necessitates  extensive  cutting  into  healthy  tooth  structure 
and  has,  as  a  result,  caused  many  operators  to  disapprove  of 
the  metallic  inlay  as  a  means  of  filling  teeth. 

Before  entering  into  the  question  of  the  proper  thickness 
of  the  cement  layer,  the  influence  of  the  box-shape  on  retention 
will  be  discussed.  As  the  conditions  for  cement-retention  in 
saucer-shaped  cavities  are  unfavorable,  and  the  inlay  itself 
has  no  anchorage  in  the  tooth,  direct  pressure  on  its  surface 


37 


will  force  the  inlay  it  out  of  the  cavity  (Fig.  35).  If  the  cavity 
is  box-shaped,  the  inlay  cannot  be  dislodged  in  this  way 
(Fig.  36).  Not  alone  does  the  inlay  here  find  a  hold  in  the 
cavity,  but  the  conditions  for  cement-retention  are  as  perfect 


Fig.   35. 


Fig.  36. 


as  possible.  The  theoretically  correct  undercuts  (Fig.  10)  may 
be  employed,  with  the  certainty  that  the  cement-retention 
will  not  fail.  The  success  of  this  form  of  cavity  is  based  upon 
the  fact,  that  the  walls  of  the  cavity  lie  farallel  to  the  direction 
in  which  the  inlay  can  he  removed  from  the  cavity.  This  funda- 
mental rule  should  be  observed  in  the  manner  described  later, 
in  preparing  all  inlay  cavities. 

"Box-shaped"  does  not  suggest  the  same  form  to  every 
operator.    A  cavity  such  as  Fig.  37,  has  been  so  designated. 


Fig.  37. 

But  in  spite  of  the  straight  walls  and  vertical  floor,  such  a 
cavity  possesses  most  of  the  physical  characters  of  the  ordinary 
saucer-shaped  cavity.  According  to  the  opinion  of  the  writer, 
the  characteristic  feature  of  the  box-shaped  cavity,  is  the 
presence  of  walls,  parallel  to  the  direction  of  removal  of  the 
inlay  (Fig.  38).  The  general  form  of  the  cavity  is  immaterial. 
The  floor  need  not  be  horizontal,  nor  need  the  angles  at  this 
point  be  sharp,  as  usually  shown  in  illustrations. 


38 


There  are  some  places  where  it  is  impossible  to  prepare 
a  cavity  box-shaped,  in  the  strictest  sense  of  the  word.  §uch 
a  cavity  with  four  parallel  walls  cannot  be  cut  into  the  neck 


Fig.  38. 


of  a  bicuspid  (Fig.  39).  The  upper  and  lov/er  walls  of  the 
cavity  {a  and  b)  may  be  made  parallel,  but  the  lateral  walls 
(c  and  d)  must  converge  in  order  to  be  at  right-angles  to  the 
surface  of  the  tooth.    These  walls  are  therefore  not  suitable 


Fig.  39. 

for  cement-retention.  The  walls  a  and  h,  lying  opposite  each 
other,  have  the  proper  direction  and  are  of  considerable  length. 
If  these  are  correctly  undercut,  sufficient  anchorage  for 
cement-retention  will  be  obtained.  If  the  pulpal  wall  of  the 
cavity  c — d  (Fig.  39)  is  convex  or  even  straight,  and  it  is  not 
deemed  advisable  to  further  weaken  the  neck  of  the  tooth 


by  extending  the  cavity  (Fig.  40,  a),  another  method  of  pre- 
venting lateral  dislocation  may  be  used.  At  a  and  b,  Fig.  41, 
broad  notches  are  cut  into  the  inlay.  These  should  lie  at 
right-angles  to  the  direction  in  which  the  inlay  can  be  dis- 
lodged. If  the  pulp  is  sufficiently  distant,  grooves  (e  and  /, 
Fig.  42)  may  also  be  cut  into  the  tooth.    The  latter  should 


Fig.   40. 


Fis.  41. 


Fig.  42. 


Fig.  43. 


be  wider  than  those  in  the  inlay,  to  allow  for  the  difficulty 
in  bringing  these  undercuts  into  exact  apposition.  The  cement 
filling  out  the  grooves  acts  as  an  inclined  plane,  changing 
the  direction  of  pressure  applied  laterally,  so  that  the  inlay 
seeks  to  escape  in  the  direction  c,  (Fig.  41).  The  cement- 
anchorage  on  the  upper  and  lower  walls  {a  and  h,  Fig.  39), 
is  sufficiently  strong,  however,  to  prevent  the  inlay  from  being 
forced  out  in  this  direction. 

Instead    of    the    anchorage    illustrated   in   Fig.  40,    that 


40 

shown  in  Fig.  43  may  be  used,  if  the  pulp  is  sufficiently 
distant.  Of  these  forms  (Figs.  40 — 43),  several  may  be  em- 
ployed in  the  retention  of  a  single  inlay.  The  presence  of  the 
anchorage  Fig.  40  or  43  on  one  end  is  desirable;  it  acts  as 
a  guide  in  setting  the  inlay  into  the  cavity. 

From  the  above  explanation,  it  becomes  evident,  that  a 
complete  box -shaped  cavity  is  not  always  possibile,  nor 
is  it  necessary  for  the  retention  of  even  a  simple  inlay.  In 
certain  places,  however,  where  the  inlay  is  exposed  to  the 
force  of  mastication,  the  complete  form,  with  four  walls, 
should  be  used.  This  refers  especially  to  inlays  on  abraded 
surfaces.  In  preparing  such  cavities  the  following  fact  should 
always  be  remembered.  Two  walls,  opposite  each  other,  and 
lying  parallel  to  the  direction  of  removal  of  the  inlay,  are  of 
far  greater  value  than  four  walls  lying  obliquely  to  this  direction. 

The  application  of  the  box-shape  to  complex  cavities  of 
molars  and  bicuspids  has  occasioned  much  adverse  criticism. 
For  this  exaggerated  type  of  cavity,  there  are  neither  practical 
nor  mechanical  reasons,  and  its  acceptance  as  the  correct 
cavity-form  for  metal-inlays,  has  caused  many  operators  to 
question  the  value  of  this  method  of  filling  teeth.  In  simple 
cavities  the  box-shape  is  employed  to  give  the  inlay  a  certain 
amount  of  mechanical  anchorage  in  the  tooth.  In  complex 
cavities,  however,  there  are  so  many  other  forms  of  anchorage 
to  select  from,  that,  in  the  opinion  of  the  writer,  an  exact 
box-shaped  preparation  becomes  quite  unnecessary. 

Many  authors  have  advocated  making  the  cement  layer 
between  inlay  and  tooth  in  the  depth  of  the  cavity,  as  thin 
as  possible,  believing  that  under  such  conditions  cement  would 
be  less  liable  to  fail  as  a  retentive  agent.  The  fact  however 
remains,  that  any  force  exerted  upon  the  inlay  is  transmitted 
to  the  tooth  through  the  cement  layer,  and  that  the  force 
which  a  self-retentive  inlay  can  resist  is  dependent  upon  the 
crushing-strength  of  the  cement.  Not  the  thickness  of  the  layer, 
but  the  quality  of  the  cement,  is  the  determining  factor,  as 
can  be  seen  from  the  following  test. 

Into  the  rough -walled  chamber  of  the  metal  block  B 
(Fig.  44),  a  roughened  metal  plug  Z  is  set  with  cement,  and 


41 

the  parts  suspended  as  shown  in  the  diagram.  By  gradually 
increasing  the  weight  on  the  scale-pan,  the  exact  tension 
necessary  to  cause  a  failure  of  the  cement  layer  is  determined. 
If  in  a  subsequent  test,  the  block  is  made  of  cement  instead 
of  metal,  the  plug  occupying  the  exact  relative  position  as 
in  the  previous  test,  the  weight  supported  will  be  the  same 
or  even  greater.  If  instead  of  tension,  pressure  is  applied  to 
the  plug,  the  tests  with  the  metal  and  the  cement  block  will 


Fig.  44. 


give  the  same  result.  The  force  necessary  will  however  be 
much  greater,  as  the  crushing  strength  of  cement  is  about 
ten  times  that  of  its  tensile  strength.  The  conclusions  to  be 
drawn  from  these  experiments  are,  that  a  thin  cement  layer 
offers  no  advantage,  and  that  the  box-shape  of  a  cavity, 
except  at  the  margin,  may  be  produced  by  cement.  Practi- 
cally this  is  of  importance  in  cavity-preparation,  as  it  often 
prevents  the  sacrifice  of  healthy  tooth  substance.  The  above 
tests  emphasize  a  point  to  which  attention  has  been  called 
in  Chap.  Ill,  that  is,  in  using  cement  as  a  retentive  agent 
the  undercuts  should  be  so  placed  and  of  such  shape,  that 
the  crushing  strength  and  not  the  tensile  strength  of  the 
cement  is  relied  upon. 

As  a  result  of  making  the  cavities  box-shaped  and  the 
cement  layer  as  thin  as  possible,  the  inlay  itself  became  box- 
shaped. 


42 

A  careful  consideration  of  Fig.  45  will  show  that  the 
direction  of  the  walls  in  the  defth  of  the  cavity,  has  no  in- 
fluence upon  the  retention  of  a  box-shaped  inlay,  as  soon  as 
the  intervening  space  is  filled  with  cement.  Far  different, 
however,  will  be  the  result,  if  in  a  box-shaped  cavity  the 
direction  of  the  lateral  walls  of  the  inlay  are  altered  (Fig.  46). 


Fig.  45. 


Fig.  46. 


The  greater  the  inclination  of  these  surfaces,  the  more  un- 
favorable will  be  the  conditions  for  retention  by  means  of 
cement  (see  Figs.  33 — 35).  The  good  results  which  the  box- 
shaped  cavity  preparation  has  shown,  depend,  in  the  opinion 
of  the  writer,  less  upon  the  form  of  the  cavity,  than  upon 
the  box-shape  of  the  inlay. 

Equally  applicable,  is  this  principle  to  the  complex  cavities 
of  the  molars  and  bicuspids.  In  the  case  of  simple  cavities 
it  has  been  shown,  that  the  superiority  of  the  box-shaped 


43 

inlay  depends  upon  the  presence  of  at  least  two  surfaces  lying 
on  opposite  sides  of  the  inlay,  and  being  parallel  to  the  direction 
in  which  the  inlay  may  he  removed  from  the  cavity.  By  applying 
this  simple  rule  to  the  most  complex  cavities  of  the  molars  and 
bicuspids,  perfect  retention  can  be  readily  obtained,  and  the 
unnecessary  removal  of  healthy  tooth-structure  avoided.  In 
describing  the  application  of  this  principle  to  such  cavitives, 
a  lower  molar  with  an  occluso-proximal  cavity  has  been 
chosen  as  an  example.  The  retention  is  to  be  obtained  by 
means  of  fissure-anchorage.  Fig.  48  shows  a  section  through 
tooth  and  inlay,  Fig.  49  shows  the  form  of  the  inlay  on  the 
occusal  surface.  For  convenience  of  explanation  the  longitu- 
dinal fissure  has  not  been  completely  filled.  In  practice  this 
should  never  be  omitted. 

Mention  has  been  made  of  the  fact,  that  a  proximal  inlay 
extending  to  the  occlusal  surface,  must  be  able  to  resist 
pressure  in  two  directions,  vertically  and  obliquely.  The  first 
is  produced  by  the  closure  of  the  jaws  and  tends  to  force 
the  inlay  out  of  the  cavity  in  the  direction  of  the  neck  of 
the  tooth;  the  second,  produced  by  masticatory  movements, 
tends  to  pry  out  the  inlay  in  the  direction  of  the  interproximal 
space. 

To  give  an  inlay  resistance  to  vertical  pressure,  the  authors 
in  whose  opinion  the  box-shaped  cavity  preparation  should 
be  strictly  carried  out,  advocate  making  as  many  surfaces 
as  possible  at  right  angles  to  the  direction  of  pressure  (Figs.  47 
and  66).  This  in  itself  is  perfectly  correct.  It  gives  the  inlay 
a  secure  base;  and  in  transmitting  the  force  from  the  inlay 
to  the  tooth  it  puts  the  cement  layer  under  compression, 
and  not,  as  in  the  molar  of  Fig.  57,  under  tension.  But  it  is 
questionable  whether  the  practive  of  giving  an  inlay  such 
an  unnecessarily  great  power  of  resistance  to  vertical  pressure 
is  justifiable,  if  this  is  done  by  the  removing  large  quantities 
of  healthy  tooth  structure. 

Fig.  17  shows  how  vertical  pressure  may  dislodge  an  inlay 
resting  upon  a  narrov/  cavity  floor.  In  Fig.  18,  to  avoid  this 
danger,  the  floor  of  the  cavity  has  been  broadened,  i.  e.,  a  larger 
surface  lying  at  right  angles  to  the  direction  of  pressure  has 


44 

been  produced.  It  is,  however,  not  necessary,  nor  in  larger 
cavities  advisable,  to  place  the  whole  of  this  bearing  surface 
upon  the  gingival  wall  of  a  proximal  cavity.  A  more  favorable 
distribution  of  these  surfaces  will  be  discussed  later.  Strict 
box-shaped  cavity  preparation  demands,  that  the  floor  of  a 
proximal  cavity  be  prepared  in  the  form  of  steps.  This  be- 
sides being  difficult  and  tedious,  requires  the  unnecessary 
destruction  of  tooth  substance. 


Fig.   47.      (From  a  dental  journal.) 

Inclined  grooves  (Fig.  21)  increase  the  bearing  surface  of 
the  inlay.  As  in  this  case  the  inlay,  under  pressure,  acts  as 
a  wedge,  the  lateral  walls  of  the  cavity  must  be  very  strong. 
To  some  extent  this  pressure  may  be  relieved  by  giving  the 
inlay  a  broad  bearing  surface  upon  the  gingival  wall  of  the 
cavity.  It  is  however  advisable  to  confine  the  use  of  this 
method  of  giving  inlays  the  power  of  resisting  vertical  pressure, 
to  the  smaller  proximal  cavi titles. 

There  remains  another  method  by  which  the  bearing  sur- 
face of  an  inlay  may  be  increased,  and  that  is  the  fissure 
anchorage.    This  method  has  several  advantages. 


45 

1.  By  cutting  out  the  fissure,  the  surface  effective  in 
resisting  vertical  pressure  is  increased. 

2.  As  this  is  done  upon  the  grinding  surface,  the  pre- 
paration is  easier,  quicker,  and  less  painful  than  cutting 
steps  or  broadening  the  wall  of  the  cavity  at  the  neck 
of  the  tooth. 


Fig.  48. 


3.  By  filling  the  fissures,  caries  will  be  prevented. 

4.  By  means  of  a  specially  prepared  pit  in  the  fissure 
{a,  Fig.  48)  or  by  an  extension  in  the  transverse  fissure 
(e,  e,  Fig.  49),  the  inlay  gains  additional  resistance  to 


Fie-.   49. 


vertical  pressure.  Only  by  fracturing  the  tooth  in  the 
direction  a — h  (Fig.  48)  or  e — f  (Fig.  49),  can  vertical 
pressure  dislodge  the  inlay.  The  amount  of  pressure  which 
an  inlay  of  this  form  can  resist,  is  dependent  upon  the 
depth  of  the  pit  a;  the  length  of  the  extension  e — e; 
the  strength  of  the  connection  d,  lying  in  the  longitu- 
dinal fissure ;  and  upon  the  strength  of  the  tooth-struc- 


46 

ture  between  the  points  a  and  h,  or  e  and  /.    The  area 
of  the  floor  of  the  proximal  cavity  is  of  but  little  con- 
sequence in  this  method  of  retention.    As  a  result,  the 
wall  h — a  (Fig.  48)  need  not  be  vertical,  as  in  true  box- 
shaped  cavity  preparation,  thereby  preserving  a  thicker 
layer   of   dentine   over  the  horns  of  the  pulp  without 
decreasing  the  resistance  of  the  inlay  to  vertical  pressure. 
Special  attention  must  be  called  to  the  fact  that  in 
this   method   of  cavity  preparation,   the  depth  of  the 
pit  a,  or  the  length  of  the  extention  e — e,  and  the  strength 
of  the  connection  d,  should  stand  in  direct  ratio  to  the 
length  and  inclination  of  the  wall  h  c. 
5.  Beside  the  above  mentioned  advantages,  this  form  of 
inlay    offers    the    most    secure    anchorage    against   the 
oblique  pressure  caused  by  the  movements  of  masti- 
cation. 
In  the  previous  chapter  the  different  forms  of  anchorage, 
designed  to  resist  oblique  pressure,  v/ere  described.   It  is,  how- 
ever, necessary  to  explain  the  application  of  the  principle  — 
walls  farallel  to  the  direction  of  removal  of  the  inlay,  —  to  this 
class  of  retention.   Fig.  18  shows  the  manner  in  which  an  inlay 
is  tipped  out  of  the  cavity  by  oblique  pressure.    It  has  been 
mentioned  that  this  may  be  prevented  by  the  fissure-anchorage. 
If  the  cavity  has  been  prepared  in  the  manner  shown  in  Fig.  50, 
the  inlay  will  be  able  to  successfully  resist  the  vertical  pressure. 
If  oblique  pressure  be  brought  to  bear  on  the  point  a.  Fig.  51, 
the  inlay  will  be  tipped  out  of  the  cavity.    Pressure  exerted 
upon  the  proximal  surface  (Fig.  52),  by  hard  particles  of  food 
wedging  against  the  neighbouring  tooth,  or  by  forcing  a  tooth- 
pick into  the  interproximal  space,  may  cause  a  dislocation  of 
the  inlay.    In  this  form,  the  fissure-anchorage  does  not  meet 
the  requirements  of  the  case. 

The  inlay  must  be  so  constructed  that  it  can  be  removed 
from  the  cavity  in  hut  one  direction.  Preferably  this  direction 
is  to  be  so  chosen,  that  it  is  opposed  to  that  of  the  ver- 
tical pressure.  In  order  that  an  inlay  may  be  guided  in  but 
one  direction  during  its  removal  from  the  cavity,  it  must  possess 
two  surfaces  which  are  opposite  each  other  and  parallel  to  the 


47 


direction  of  removal  of  the  inlay.  Fig.  53  shows  that  these 
parallel  surfaces  may  be  situated  at  a  and  h,  h  and  c,  or  on  the 
same  inlay  at  a,  h,  and  c.  An  inlay  of  this  form  can  be  dislodged 


Fis;.  50. 


Fig.  51. 


Fig.  52. 


neither  by  vertical  nor  by  oblique  pressure,  as  the  parallel 
walls  form  a  guide  which  allows  the  inlay  to  be  removed 
only  in  the  direction  of  the  arrow.    The  presence  of  these 


guide-surfaces  is  essential  in  every  case,  their  size,  however, 
in  order  to  oppose  the  oblique  pressure  need  not  be  large. 
This  question  will  again  be  referred  to  in  discussing  the  cement 
attachment  of  this  class  of  inlays. 


48 

The  office  of  the  cement  as  a  retentive  agent  for  inlays 
in  proximal  cavities  has  not  as  yet  been  touched  upon.  Many 
inlays  doing  service  for  a  long  period  of  time  in  carefully 
prepared,  but  mechanically  incorrectly  shaped  cavities,  owe 
their  retention  entirely  to  the  cement  (Fig.  57).  The  same  is 
true  of  some  inlays  in  cavities  prepared  strictly  according  to 
the  box-shaped  principle  (Fig.  66). 

In  certain  proximal  cavities  of  the  posterior  teeth,  it  is 
justifiable  to  disregard  the  mechanical  anchorage,  and  to 
depend  entirely  upon  the  cement  for  retention.  Such  cavities, 
facing  the  space  caused  by  an  extraction,  have  their  greatest 
diameter  at  the  neck  of  the  tooth,  and  involve  but  little  of 
the  occlusal  surface  (Fig.  54).    To  prepare  the  cavity  so,  that 


Fig.  54. 


the  impression  could  be  removed  only  in  the  direction  con- 
trary to  that  of  the  vertical  pressure,  would  be  useless  labor 
and  an  unnecessary  destruction  of  tooth-substance.  The  prac- 
tice of  extension  for  prevention  would  not  be  indicated  in 
this  case,  as  there  is  no  contact  with  an  adjoining  tooth. 

If  the  impression  is  removed  from  the  cavity  in  the  direction 
of  the  space,  the  construction  of  a  self-retentive  inlay  becomes 
impossible.  It  is  therefore  upon  the  cement  that  complete 
reliance  must  be  placed.  With  a  properly  shaped  inlay,  this 
mode  of  retention  may,  however,  be  relied  upon.  The  fact 
that  the  inlay  possesses  a  small  occlusal  surface  (Fig.  54), 
may  be  disregarded,  and  the  cavity  considered  as  a  simple 
one,  lying  on  the  proximal  surface  of  the  tooth.  It  has  been 
shown  that  sufficient  retention  can  be  given  an  inlay,  by 
constructing  two  of  its  surfaces  parallel  to  the  direction  of 


49 

removal.  In  the  present  case  this  direction  would  be  toward 
the  space,  as  the  oblique  pressure  would  tend  to  tip  the  inlay 
out  of  the  cavity.  In  discussing  mechanical  anchorage  it 
was  shown,  that  to  prevent  dislocation,  the  hold  should  be 
applied  as  high  as  possible,  that  is,  as  far  away  from  the 
fulcrum  of  the  leverage  as  circumstances  will  permit  (Fig.  21). 
The  preparation  of  the  parallel  walls  a  and  h  (Fig.  54)  is  begun 
at  the  occlusal  surface  and  continued  as  far  as  possible  in  the 
direction  of  the  neck  of  the  tooth,  constantly  keeping  in  mind 
that  they  are  to  be  made  parallel  to  the  direction  in  which 
the  inlay  could  be  tipped  out  of  the  cavity.  It  is  not  necessary 
to  make  the  walls  parallel  to  the  points  c,  as  the  chief  hold 
lies  at  a  and  h.  The  gingival  wall  of  the  cavity  should,  however, 
be  broad  and  horizontal,  in  order  to  oppose  the  vertical 
pressure. 

Whether  the  inlay  should  be  regularly  undercut  or  simply 
roughened,  must  be  decided  from  case  to  case.  If  the  parallel 
surfaces  a  and  h  are  small,  or  ii  the  occlusal  surface  of  the  inlay 
is  large,  regular  undercuts  should  be  employed.  If  the  con- 
trary is  the  case,  simple  roughening  will  give  ample  security. 
As  a  rule,  it  is  best  to  make  short  undercuts  at  a  and  h,  lying 
at  right  angles  to  the  direction  in  which  the  inlay  can  tip, 
and  to  employ  the  step-like  roughening  (Fig.  14)  upon  the 
remaining  surfaces.  Bevelling  the  occlusal  surface  toward  the 
space,  is  to  be  recommended  (Fig.  16);  instead  of  being  tipped 
out,  the  inlay  is  then  pressed  into  the  cavity  more  firmly 
by  the  vertical  pressure. 

The  principles  just  described  are  applicable  not  only  to 
the  posterior  teeth,  but  to  proximal  cavities  of  other  teeth 
as  well.  Inlays  constructed  in  this  manner  do  very  good 
service,  but  as  a  rule  the  anchorage  of  all  larger  inlays  in  the 
bicuspids  and  molars  should  depend  upon  self-retention. 

Th3  office  of  the  cement,  in  retaining  a  correctly  con- 
structed, self-retentive  inlay  in  the  cavity,  is  confined  to  a 
filling  out  of  all  spaces  between  the  inlay  and  the  tooth,  and 
to  the  prevention  of  dislodgement  in  the  direction  of  removal. 
In  discussing  Fig.  53,  it  was  stated  that  the  parallel  surfaces 
a  and  h  need  not  be  large  in  order  to  resist  the  obUque  pressure. 

Tiddecker,  Metallic  Inlay.  4 


50 

For  a  reliable  cement  attachment,  these  surfaces  alone  are, 
however,  too  small.  Only  such  surfaces  which  lie  on  sides 
opposite  each  other,  and  which  are  parallel  to  the  direction  of 
removal,  are  suitable  for  cement-retention.  If  no  other  sur- 
faces of  this  description  are  present  upon  the  inlay,  the  trans- 
verse fissure  must  be  deepened  considerably  to  increase  the 
area  of  the  surfaces  a  and  h  (Fig.  53). 

In  a  cavity  whose  buccal  and  lingual  walls  are  lacking 
(Fig.  49)  and  whose  axial  wall  is  inclined  (c,  h,  Fig.  48),  the 
parallel  surfaces  may  be  made  upon  the  connecting  segment 
of  the  inlay  lying  in  the  longitudinal  fissure   at  d  (Fig.  48 


Fig.   55. 

and  49).  The  depth  of  excavation  necessary  in  the  transverse 
fissure  {a.  Fig.  48  or  e — e.  Fig.  49)  depends  upon  the  area  of 
the  surfaces  g  and  Ji  (Fig.  49),  and  the  inclination  of  the  axial 
wall  c — h  (Fig.  48).  If  the  parallel  surfaces  are  small,  regular 
undercuts  are  necessary  at  these  points  for  reliable  cement- 
retention  (Fig.  10).  As  a  rule  however,  roughening  the  sur- 
face of  the  inlay  as  shown  in  Fig.  14  is  sufficient. 

In  case  the  lingual  and  buccal  walls  of  the  cavity  have 
been  preserved,  the  parallel  surfaces  on  the  inlay  should  be 
situated  there.  By  virtue  of  the  fact,  that  the  inlay  can  be 
removed  in  but  one  direction,  the  proximal  part  may  be  con- 
sidered as  a  simple  cavity  opening  upon  the  occlusal  surface. 
If  then,  the  walls  a  and  h  (Fig.  55)  are,  for  a  short  distance, 
made  parallel  to  the  direction  of  removal,  ideal  conditions 
for  cement-retention  will  have  been  produced.  If  the  axial 
wall  is  inclined,  the  surfaces  a  and  h  should  be  increased  in 


51 


area.  If  the  axial  wall  is  vertical,  and  the  walls  a  and  h  cor- 
rectly prepared,  deep  excavation  will  become  unnecessary  in 
transverse  fissure  (e — e,  Fig.  49), 

Regular  undercuts  are  not  necessary  in  this  class  of  inlays. 
That  part  of  the  inlay,  lying  in  the  fissure,  is  roughened  by 
blows  at  right-angles  to  the  surface  (Fig.  13).  The  surface 
of  the  inlay,  lying  within  the  proximal  cavity,  is  roughened 


Fig.  56. 


by  an  obliquely  applied  instrument  (Fig.  14).  As  this  throws 
up  small  projections,  thereby  slightly  increasing  the  size  of 
the  inlay,   a  thin  layer  of   dentine   should  be  removed  from 


Fig.   57.      (From  a   dental  journal.) 

the  walls  of  the  cavity  at  the  points  opposite  to  the  surfaces 
so  roughened. 

In  discussing  the  fundamental  principles  of  retention,  only 
certain  cavities  of  the  molars  and  bicuspids  have  been  cited 
as  examples,  as  these  are  the  ones  most  commonly  filled  with 
metallic  inlays.  The  application  of  the  principles  to  other 
cavities  is  perfectly  simple  if  the  reader  has  understood  the 
writer's  ideas  upon  the  subject  of  cement-retention  and  self- 
retentive  inlays. 


52 

Before  leaving  this  subject,  a  few  examples  of  inlays  with 
insufficient  retention  will  be  given.  Fig.  56  shows  a  form  of 
anchorage  which  has  been  repeatedly  recommended.  Without 
going  into  details,  it  is  only  necessary  to  call  attention  to  the 
fact,  that  an  inlay  of  this  form  cannot  resist  oblique  pressure, 
as  the  hold  it  has  on  the  tooth  (the  extension)  is  situated  very 
close  by  to  the  fulcrum  of  the  leaverage.  Among  the  hollow 
inlays  many  examples  of  insufficient  retention  may  be  found 
(Fig.  57).  In  filling  out  the  space,  the  cement  gains  a  firm 
hold  on  the  inlay ;  the  hold  upon  the  tooth,  however,  is  entirely 
dependent  upon  the  adhesive  power  of  the  cement.  Granting 
the  latter  to  be  sufficiently  strong,  the  retention  of  the  inlay 
then  depends  upon  the  tensile  strength  of  the  cement,  and 
this,  as  has  been  previously  mentioned,  is  not  very  great. 


Chapter  V. 
Caries  and  Cavity-Form. 

Though  this  subject  has  been  thoroughly  discussed  in  text- 
books on  operative  dentistry,  it  is  deemed  advisable  to  empha- 
size certain  points  which  should  be  considered  in  preparing 
cavities  for  metallic  inlays.  Experience  has  shown,  that  it  is 
not  necessary  to  remove  any  more,  and  sometimes  even  less, 
tooth-substance  in  preparing  a  cavity  in  which  a  metallic 
inlay  is  indicated,  than  in  preparing  the  same  cavity  for  a 
perfect  gold  foil  filling.  For  comparison,  the  cavity  preparation 
for  foil  fillings  as  advocated  by  G.  V.  Black*),  has  been  chosen. 

In  preparing  a  cavity,  the  fact  should  never  be  overlooked, 
that  the  office  of  a  perfect  filling  is  not  alone  to  restore  the 
destroyed  parts,  but  that  it  should  also  protect  the  tooth  at 
that  point  from  recurrent  caries.  For  this  reason,  it  has 
become  a  recognised  practice  in  filling  the  fissures  on  the 
occlusal  surfaces  of  the  posterior  teeth,  to  excavate  the  affected 
fissure  throughout  its  whole  length.  To  what  extent  this 
principle  should  be  applied  to  the  proximal  cavities  is  a  mooted 
question.  Theoretically  the  practice  is  justifiable,  practically, 
however,  experience  has  proven  that  it  is  not  always  necessary. 

The  point  of  origin  of  dental  caries  is  either  a  fissure,  or  a 
smooth  surface  protected  from  the  cleansing  action  of  masti- 
cation. The  course  of  the  carious  process  is  dependent  upon 
its  point  of  origin.  Caries  in  enamel,  as  well  as  in  dentine, 
progresses  in  the  form  of  a  wedge.  In  caries  of  the  fissures, 
the  points  of  the  wedges  lie  in  opposite  directions  {a,  Fig.  58). 
In  the  enamel  the  process  is  somewhat  limited,  while  in  the 
dentine,  owing  to  the  less  resistant  dentine-enamel  margin, 
the  spread  of  caries  is  far  more  rapid.    The  effected  area  of 


*)   G.  V.  Black,   Operative   Dentistry,  Vol.  II. 


54 


the  dentine  is  therefore  considerably  larger  than  that  of  the 
enamel.  - 

In  caries  beginning  upon  smooth  surfaces,  the  points  of 
the   affected   wedge-shaped   areas   lie   in   the   same   direction 


Fig.  58  (after  Black). 


i 


Fig.   59   (after  Black). 


[h.  Fig.  58,  a  and  h,  Fig.  59).  In  contradistinction  to  caries 
of  the  fissures,  the  area  of  the  enamel  involved  is  larger  than 
that  of  the  dentine.  This  is  explained  by  the  fact,  that  the 
agents  producing  caries  can  more  easily  attack  the  surface 
of  the  enamel  at  more  protected  points  than  upon  the  self- 
cleansing  occlusal  surface  of  the  teeth. 

An  examination  of  Fig.  58  proves,  that  a  broad  excavation 


55 


of  the  fissures  is  perfectly  justified  on  account  of  the  spread 
of  the  caries  along  the  dentine -enamel  margin.  This  is  of 
advantage  to  the  inlay,  as  thereby  the  extensions  lying  in 
the  fissures  are  greatly  strengthened,  thus  giving  the  inlay 
a  firmer  anchorage  in  the  tooth. 

The  writer  considers  the  box-shaped  cavity,  as  usually 
recommended,  not  at  all  necessary  for  an  inlay.  It  requires 
extra  labor  and  a  useless  destruction  of  tooth  substance,  some- 
times to  such  an  extent  as  to  endanger  the  horns  of  the  pulp. 
A  cavity  prepared  in  the  tooth  Fig.  58,  would  fulfill  all  require- 
ments, if  it  had  the  form  shown  in  Fig.  60.  The  course  of  the 
enamel  prisms  is  such  that  the  cavity  margin  need  not  be 
bevelled.     This   gives   the   inlay   two   parallel   surfaces   lying 


Fig.  60  (Black). 


Fig.   61   (Black). 


Fig.   62  (Black). 


opposite  eachother,  which  is  amply  sufficient  for  cement- 
retention.  The  impression  can  be  more  easily  removed  from 
this  form,  than  from  a  box-shaped  cavity. 

If  the  cavity  (Fig.  60)  is  to  be  filled  with  gold,  the  floor 
must  be  made  flat.  If  this  is  done  at  right-angles  to  the 
deepest  point,  the  form  shown  in  Fig.  61  will  result.  This 
would  probably  endanger  the  horns  of  the  pulp.  To  avoid 
this  danger.  Black  advocates  cutting  a  ledge  a  little  above 
the  deepest  part  of  the  cavity  (Fig.  62).  For  an  inlay  this 
form  of  cavity  offers  no  advantage  over  that  of  Fig.  60. 
Besides  being  a  loss  of  time,  cutting  the  ledge  increases  the 
danger  of  making  undercuts  in  the  walls  of  the  cavity.  It  is 
just  in  the  fissure  cavities,  where  the  amount  of  the  material 
is  small,  that  the  slightest  undercut  may  produce  distortion 
during  the  removal  of  the  impression. 

The  preparation  of  box-shaped  cavities  upon  the  smooth 


56 

surfaces,  necessitates  a  still  greater  destruction  of  tooth-sub- 
stance than  is  the  case  in  fissure  cavities.  This  becomes 
evident  in  examining  cervical  caries  on  the  buccal  surface  of 
a  lower  molar.  Caries  at  this  point  spreads  in  a  horizontal 
direction    (h,    Fig.  59),    while    vertically    it    remains    limited 


Fig.  63. 


Fig.  64. 


Fig.  65. 


(£,  Fig.  58).  Instead  of  box-shaped  (Fig.  63),  such  a  cavity 
may,  without  endangering  the  retention,  be  prepared  almost 
saucer-shaped  in  the  horizontal  direction  (Fig.  64)  as  long  as 
the  vertical  section  shows  two  parallel  walls,  lying  opposite 
each  other  (Fig.  65). 

Proximal  cavities  prepared  along  similar  lines,  also  show 
the  same  advantage.  A  box-shaped  cavity  cut  into  the  tooth 
at  a  (Fig.  59),  would  require  the  removal  of  a  considerable 
quantity  of  healthy  dentine.    By  preparing  such  a  cavity  in 


57 


the  maimer  described  (Plate  I),  this  needless  destruction  is 
obviated.  A  vertical  section  through  the  proximal  cavity 
shows  that  it  is  necessary  to  remove  less  tooth-substance  in 
preparing  a  cavity  for  a  metallic  inlay  than  in  preparing  the 
same  cavity  for  a  foil  filling.  The  inlay  has  the  following 
advantages:  The  gingival  wall  of  the  cavity  need'  neither  be 
large  nor  perfectly  horizontal  (Fig.  48);  the  cavity  walls  need 
not  meet  at  sharp  angles;  and  the  axial  wall  need  not  be 


Fig.   66.     (From  a  dental  journal. 


vertical.  These  requirements  not  only  denote  a  saving  of  tooth- 
substance,  but  they  also  make  cavity  preparation  considerably 
less  difficult. 

To  what  extremes  the  advocates  of  strictly  box-shaped 
cavity  preparation  have  gone,  is  shown  in  Fig.  66.  In  the 
preparation  of  this  cavity,  intended  for  a  bridge-abuttment, 
the  vertical  pressure  to  which  the  inlay  is  subjected,  has 
almost  exclusively  been  taken  into  account.  The  oblique 
pressure,  caused  by  the  movements  of  mastication,  has  received 
but  little  attention.    Neither  the  grooves  a,  a  (Fig.  66),  nor 


58 

undercuts  can  give  sufficient  anchorage  to  prevent  the  leverage, 
which  is  especially  great  in  a  bridge-abuttment,  from,  dis- 
locating the  inlay. 

So  far  only  those  points,  in  which  the  cavity  preparation  for 
an  inlay  differs  from  that  of  a  foil  filling,  have  been  mentioned. 
In  other  respects,  the  principles  underlying  the  preparation  of 
cavities   for   foil  fillings   and  for  metallic  inlays  are  identical. 

These  principles  will  only  be  briefly  mentioned  in  order 
to  emphasize  the  fact,  that  a  more  extensive  excavation  is 
not  necessary  for  an  inlay  than  for  a  gold  filling.  Proximal 
cavities  to  be  filled  with  inlays  must  be  extended  laterally, 
to  allow  the  impression  to  be  drawn.  This  procedure  has  been 
condemned  as  a  useless  sacrifice  of  healthy  tooth-substance. 
If,  however,  the  long  experience  of  operators  who  have  given 
this  subject  their  special  attention,  counts  for  anything,  then 
the  extended  cavity,  inevitable  to  a  certain  extent  in  an 
inlay,  represents  the  most  perfect  form  for  a  foil-filling.  This 
method  of  cavity  preparation,  the  so-called  "extension  for 
prevention*)"  of  Black,  is  a  prophylactic  measure,  pure  and 
simple,  and  never  should  be  regarded  as  anything  else.  The 
marked  difference  in  opinion  as  to  the  value  of  this  method, 
has  bred  extremists  in  each  direction.  It  is,  however,  just  as 
unreasonable  to  disregard  it  entirely,  as  to  practice  it  in  every 
case.  Being  a  prophylactic  measure,  it  should  be  practiced 
only  when  indicated. 

The  theory  of  extension  for  prevention**)  is  based  upon  the 
fact  that  caries  but  very  rarely  attacks  surfaces  cleansed  by 
the  food  during  the  act  of  mastication.  In  normally  placed 
teeth,  the  surfaces  especially  immune  to  caries  are  situated 
in  the  region  of  the  mesio-lingual,  the  mesio-buccal,  the  disto- 
lingual  and  the  disto-buccal  angles,  and  extend  from  the  neck 
to  occlusal  surfaces  of  the  teeth  (Fig.  67  and  68).  For  this 
reason,  it  is  often  advisable,  as  a  prophylactic  measure,  to 
place  the  margin  of  the  cavity  in  the  region  exposed  to  the 
cleansing  action  of  the  food. 

*)  This  term  is  here  used  in  the  most  Umited  sense,  and  does  not  include 
the  idea  of  contour  or  contact-point. 

**)  G.  V.  Black,  Operative  Dentisby. 


59 


The  cleansing  action  of  mastication  is  dependent  upon  the 
width  and  depth  of  the  embrasures  formed  by  the  surfaces 
of  adjoining  teeth.    If  the  embrasures  are  narrow,  (Fig.  69), 


Fig.   67   (Black). 

Shaded    portions    represent    areas    most    liable  to   caries.      The   continuous  black  line 

represents  the  free  margin  of  the  gum,  while  the  dotled  lines  show  its   attachment 

to  the  necks  of  the  teeth.     The  double  line  shows  the  course  of  the  saw  in  making 

the  cross-section  Fig.  68. 

the  food  ghdes  only  over  the  lingual  and  the  buccal  surfaces 
of  the  teeth,  if  on  the  other  hand,  they  are  wide  (Fig.  70) 


Fig.   68  (Black). 


a  greater  part  of  the  proximal  surfaces  are  also  cleansed.    As 
the  form   of  the  embrasure  is  dependent  upon  the  contour 


Fig.  69  (Black). 


Fig.   70  (Black). 


of  the  tooth,  it  is  necessary,  in  order  to  obtain  a  wide  embrasure, 
to  build  out  the  filling  or  inlay,  as  far  and  as  rounded  as 
possible.  Even  though  the  natural  tooth  does  not  possess  this 
rounded  contour  (Fig.  69),  it  should  be  present  on  the  finished 
filling.  As  a  rule  there  is  not  sufficient  space  for  a  contour  filHng, 


60 

and  seperation  must  be  resorted  to.  Guttapercha  as  a  slower, 
and  cotton  with  varnish  as  a  more  rapid  method,  give  good 
results.  For  immediate  seperation,  the  seperator  must  be  used. 
To  forcibly  produce  a  wide  space  at  any  point  in  the  arch, 
in  cases  where  the  teeth  stand  very  closely,  is  a  procedure 
which  the  writer  believes  to  be  injurious  to  the  other  teeth. 
Secondary  caries  will  probably  be  prevented  at  the  place  filled, 
but  the  increased  pressure  will  make  the  proximal  surfaces 
of  the  other  teeth  more  liable  to  attack.  To  produce  an  inlay 
with  a  good  contour  in  such  an  arch  without  taking  up  more 
space  than  the  tooth  originally  occupied,  the  proximal  sur- 
face should  be  ground  flat  with  a  diamond-disk  (Plate  V). 


Fig.   71   (Black). 

The  margins  of  the  cavity  then  lie  in  the  region  immune  to 
caries,  and  there  is  sufficient  space  to  give  the  inlay  a  good 
contour  without  still  more  crowding  the  arch.  The  best  results 
are  obtained  by  this  procedure  v/hen  tv/o  proximal  cavities, 
lying  opposite  one  another,  are  to  be  filled  at  the  same  time. 
With  inlays,  the  form  of  the  interproximal  space  and  that 
of  the  cervical  margin  should  be  the  same  as  with  gold  fillings. 
The  cervical  margin  should  lie  well  toward  the  margin  of  the 
gum;  should  be  horizontal;  and  not  too  short  in  the  linguo- 
buccal  direction.  It  is  not,  however,  necessary  to  make  the 
lingual  and  the  buccal  angles  as  sharp  as  is  recommended 
for  gold  fillings  (Compare  Plate  I  and  Fig.  71).  To  obtain 
sharp  angles,  burs  or  chisels  must  be  used,  and  these  are 
very  liable  to  produce  undercuts.  With  stones  of  proper  shape 
and  size,  the  proper  cavity-form  is  produced  almost  automati- 
cally. 


61 

The  shape  of  the  interproximal  space  is  determined  by 
the  distance  between  the  teeth  and  the  position  of  the  con- 
tact point.  The  latter  should  form  a  decided  eminence  (Fig.  72), 
and  not  be  gently  rounded  as  in  Fig.  73.  The  contact  point 
should  lie  just  above  the  junction  of  the  upper  and  middle 
thirds  of  the  crown  of  the  tooth  (Fig.  72).    The  inlay  should 


Fig.  72. 


Fig.  73. 


Fig.   74. 


be  as  flat  as  possible  below  the  contact  point,  as  in  Fig.  72, 
not  as  in  Fig.  73  or  74,  so  that  the  "pumplike  action"  of 
mastication  can  readily  keep  the  interproximal  space  clear. 
A  careful  consideration  of  the  facts  discussed  in  this 
chapter,  will  disprove  the  assertion,  that  the  inlay  requires 
an  unnecessary  sacrifice  of  tooth-structure,  if  the  theory  of 
extension  for  prevention  is  accepted  and  exaggerated  box- 
shaped  cavities  are  avoided. 


Chapter  VI. 
The  Enamel  Margin. 

Of  prime  importance  for  the  durabihty  of  an  inlay,  is  the 
correct  preparation  of  the  enamel  margin  of  the  cavity.  This 
margin  should  be  so  prepared,  that  it  possesses  the  greatest 
possible  resistance  to  injury  under  the  following  circumstances: 

1.  During  the  time  that  the  cavity  is  temporarily  filled, 
that  is,  between  the  time  of  taking  the  impression  and 
of  setting  the  inlay. 

2.  During  the  process  of  fitting  and  burnishing  the  inlay. 

3.  When  the  cement  has  been  slightly  dissolved  out  of 
the  seam. 

4.  In  reclosing  the  seam  by  burnishing  the  gold  against 
the  enamel  margin. 

Simply  bevelling  the  edge  does  not,  in  all  cases,  insure 
against  failure.  It  is  the  structure  of  the  enamel,  that  is,  the 
course  of  the  prisms,  that  must  be  taken  into  account.  As 
has  been  mentioned,  the  surface  of  the  cement  is  dissolved 
to  a  depth  equal  to  the  width  of  the  seam.  The  right-angled 
enamel  edge,  no  longer  supported  by  the  cement,  is  very 
liable  to  fracture.  To  prevent  this,  bevelhng  the  edge  30  to  45  ° 
has  been  advocated.  If  the  enamel  were  a  body  equally 
resistant  in  all  directions,  this  precaution  would  suffice.  The 
fact,  however,  is  that  enamel  is  easily  cleavable  parallel  to 
the  course  of  the  prisms.  If  in  preparing  the  margin,  the 
direction  of  the  prisms  is  not  accurately  noted,  a  failure  will 
result  in  certain  places  on  the  teeth  in  spite  of  the  fact  that 
the  enamel  edge  was  carefully  bevelled.  Fig.  75  shows  a  section 
through  the  margin  of  a  cavity  filled  with  an  inlay.  The 
enamel  has  been  bevelled  as  advocated.  The  prisms,  however, 
lie,  as  they  do  in  various  places  on  the  teeth,  very  obliquely 
to  the  surface.   As  long  as  the  cement  within  the  seam  remains 


63 

inta(;t,  tli(!  onamcl  cannot  fracture,  when  in  time  the  cement 
is  (lisH()]v(!(l,  the  oblique  prisms  loose  their  support,  and  are 
soon  broken  away.  The  seam  is  thereby  widened,  allowing 
a  further  solution  of  the  cement  to  take  place.  When  the 
dissolution  of  the  cement  has  reached  the  point  a  (Fig.  75), 
a  part  of  the  cnarncl,  of  the  form  h — a,  will  gradually  crumble 
away.  If  the  course  of  the  prisms  is  at  right  angles  to  the 
surface  and  the  enamel  edge  slightly  beveHed  (P'ig.  76),  the 
danger  of  fracture  is  reduced  to  a  minimum.    It  is  therefore 


Fig.  11 


Fij,'.  70. 


f'vident  that  thf;  most  favorjiljlc  position  for  tlif;  cavity  wall 
in  the  enamel  region,  is  paralle]  to  the  direction  of  the  prisms. 
This  may,  or  may  not  result  in  a  cavity  wall  lying  at  ri^^jt- 
angles  to  the  surface  of  the  tooth. 

The  operator  can  only  j^rfparf  cavities  correctly,  if  he  has 
a  thorough  knowledge  of  the  course  of  the  prisms  on  the 
surfaces  of  each  individual  tooth.  A  study  of  the  Figs.  77 — 82 
shows  that  as  a  rule  the  prisms  lie  at  right-angles  to  the  sur- 
face. Exceptions  are  ff^iind  on  thf  occlusal  surfaces  and  adja- 
cent thirds  of  the  crowns  of  the  molars  and  bicuspids.  The 
enamel  prisms  of  the  incisors,  particularly  on  the  lingual  sur- 
face (Fig.  77),  lie  Vfry  f^hliqiifly.  In  preparing  a  cavity  on 
this  surface,  the  wall  toward  the  incisive  edge,  must  be  espe- 
cially oblique  in  the  region  of  the  enamel.  The  mesial,  and 
more  markedly  the  distal  angles  of  the  cutting  edge  of  the 
incisors,  show  an  oblique  position  of  the  enamel  prisms  (Fig.  78), 
especially  in  the  upper  lateral  incisor.  In  a  cross  section  Xhrow^h 


64 


Fig.   77   (Black). 
An    axio-labio-lingual 
section  of  an  incisor. 


Fig.   78  (after  Black). 

An  axio-mesio-distal   section 

of  a  lateral  incisor. 


Fig.  79  (Black). 
"A  bicuspid  tooth  split 
bucco  -  lingnally  showing 
the  directions  of  the  ena- 
mel rods  in  the  different 
parts  of  the  plane  of  the 
cut.  The  recessional  lines 
of  the  horns  of  the  pulp  are 
shown  by  the  dotted  lines." 


Fig.  80  (Black). 
"A  mesio-distal  section  of  a  lower 
molar  tooth  showing  the  more 
usual  directions  of  the  enamel 
rods  in  the  different  parts  of 
the  plane  of  the  section." 


Fig.  81   (Black). 
Perpendicvdar  section  through 
the    cusp   of    a  molar   thooth. 


Fig.   82  (Black). 

Section  across  a  deep 

fissure. 


65 

the  middle  of  an  incisor,  the  course  of  the  prisms  is  at  right- 
angles  to  the  surface,  except  at  the  mesio-lingual  and  disto- 
lingual  angle.  Again  in  the  upper  lateral  incisor  this  con- 
dition is  most  marked.  In  the  cuspids,  the  course  of  the 
prisms  is  at  right-angles,  except  upon  the  hngual  surface, 
where  they  lie  similar  to  those  of  the  incisors  at  this  point. 

In  the  molars  and  bicuspids  the  prisms  lie  at  right-angles 
to  the  surface,  expect  in  the  regions  about  the  cusps  and  the 
fissures.  From  the  diagrams  taken  from  the  latest  work  of 
Black*),  it  appears,  that  in  preparing  a  cavity  on  the  occlusal 
surface  but  little  bevelling  of  the  margin  is  necessary  to  prevent 
cleavage  of  the  enamel.  The  most  favorable  conditions  are 
found  in  the  neighborhood  of  deep  fissures  (Fig.  82).  In  such 
cases  bevelling  the  edge  becomes  quite  unnecessary. 

These  diagrams  show  the  normal  course  of  the  prisms  at 
various  points  upon  the  teeth ;  in  practice  abnormal  conditions 
are,  however,  often  encountered.  During  the  preparation  of 
the  cavity,  the  direction  of  cleavage  can  easily  be  determined, 
if  necessary,  by  fracturing  the  edge  of  the  enamel  with  a 
sharp  chisel  and  noting  the  direction  of  the  break. 

Not  the  surface  of  the  tooth,  but  the  course  of  the  prisms 
determines  the  angle  of  the  cavity  wall  within  the  enamel 
region.  The  cavity  wall  should  be  parallel  to  the  prisms  or 
cross  their  outer  ends.  Never  under  any  circumstances  should 
the  inner  or  dentinal  end  of  an  enamel  priiim  be  needlessly  cut. 
This,  not  alone  for  mechanical,  but  also  for  physiological 
reasons. 

Morphologically  the  enamel  may  be  divided  into  two  zones, 
an  outer,  in  which  the  prisms  lie  parallel  to  eachother  and 
generally  at  right-angles  to  the  surface,  and  an  inner  in  which 
the  course  of  the  prisms  is  very  irregular  (Figs.  84  and  83). 
Cleavage  of  the  outer  zone  takes  place  easily,  of  the  inner 
zone  only  with  great  difficulty.  Usually  the  inner  zone  is  by 
far  the  broader  of  the  two.  This  is  of  interest  in  connection 
with  cavity  preparation  as  it  proves  the  danger  of  fracture 
to  be  greater  near  the  surface  of  the  enamel. 


*)  G.  V.  Black,  Operative  Dentistry,  Vol.  II. 
Bodecker,  Metallic  Inlay. 


66 


Fig.  84  shows  that  it  is  not  possible  to  cut  a  cavity  wall, 
parallel  throughout  to  the  course  of  an  enamel  prism.  The 
theoretically  correct  preparation  of  the  cavity  wall  within  the 


\    *      '-.V  ,»Y< 


>ivMi?t^mhK<:"- 


Fio-.  83. 


enamal  region  is  the  following:  in  the  inner  two-thirds  of  the 
enamel  the  wall  should  lie  parallel  to  the  direction  of  cleavage, 


Fig.  84. 


while  in  the  outer  third,  it  should  be  bevelled  slightly.  In 
practice,  however,  this  rule  can  but  rarely  be  observed,  as 
abutting  joints  should  be  avoided  on  account  of  the  con- 
traction  of  the   gold.     Upon  the  occlusal  surface  the  diffi- 


67 


ciilty  may  be  overcome  by  carving  deep  fissures  in  the  in- 
lay (wax  model).  The  edge  of  the  inlay  will  then  no  louger 
be  right-angled,  but  be  so  thin  that  it  may  easily  be  bur- 
mished  against  the  margin  of  the  enamel.  Upon  the  other 
surfaces  of  the  teeth  the  enamel  margins  should  be  bevelled 
about   45°,    unless  the  inlay  already  possesses  a  thin  edge. 


Chapter  VII. 
Instruments  for  Cavity  Preparation. 

A  description  of  all  the  instruments  required  for  the  pre- 
paration of  cavities  is  not  necessary.  Only  those  which  are 
of  special  value  in  inlay  technic  will  be  considered. 

In  preparing  a  cavity  for  an  inlay,  the  possibility  of  remov- 
ing the  impression  must  always  be  kept  in  mind.  On  account 
of  the  danger  of  undercuts  the  use  of  small  burs  or  of  in- 
struments of  unsuitable  form,  should  always  be  avoided. 
Almost  all  cavities  can  be  prepared  completely  by  the  aid 
of  stones.  Carborundum  stones  cut  rapidly,  leave  smooth 
margins,  and  if  kept  moistened  are  more  agreeable  to  the 
patient  than  steel  burs.  The  forms  most  commonly  used  are 
the  barrel-shaped,  ground  somewhat  conical  upon  a  file,  the 
spherical  and  the  thin  wheel. 

In  order  to  suit  individual  requirements,  it  is  advisable 
for  each  operator  to  mount  his  own  barrel-shaped  stones. 
If  the  mandril  possesses  a  thread,  this  should  by  ground  off 
at  two  points  opposite  another,  in  order  to  prevent  the  stone 
from  unscrewing  when  used  with  the  engine  reserved.  The 
stones  are  mounted  with  thinly  mixed  cement.  A  number 
may  be  mounted  at  the  same  time  as  they  must  all  be  trued 
later.  After  the  cement  has  hardened  the  mandril  is  mounted 
in  a  lathe,  and  the  stone  trued  up  with  a  file,  and  any  desired 
special  form  produced.  If  no  lathe  is  handy,  the  stones  may 
be  trued  under  moisture,  on  the  engine.  Care  should  be  taken 
that  no  water  mixed  with  carborundum  is  drawn  up  into  the 
hand-piece.  Before  grinding,  the  mandril  should  be  well  covered 
with  vaseline.  Dry  grinding  is  equally  dangerous,  as  the 
carborundum  dust  rapidly  wears  out  the  hand-piece.  Instead 
of  a  file,  the  instrument  shown  in  Fig.  84  a,  may  be  used.  The 
stone  is  cut  by  an  adjustable  diamond  point. 


69 

Barrel  shaped  stones  can  be  obtained  in  sevoral  sizes.  The 
most  practical  is  about  ^^  inch  long  and  of  about  the  same 
diameter  (Fig.  85).  With  a  file,  the  stone  is  formed  as  shown 
in  Fig.  86.    Wear  constantly  decreases  the  diameter  of  the 


Fig.  84  a. 


stones,  making  the  preparation  of  stones  of  different  sizes 
unnecessary.  If  the  tip,  in  time  becomes  too  pointed,  it  should 
be  squared  with  a  carborundum  wheel  (Fig.  87).  Small  zylindri- 
cal  stones,  in  shape  similar  to  large  fissure  burs,  and  sold 

9)1  9 


Fis.  85.  Fig.  86. 


Fig.  87. 


Fig.  88. 


under  the  name  of  Miller's  points  (Chicago),  are  often  of 
service.  Small  round  stones,  about  an  ^/g  inch  in  diameter 
are  indispensible  for  finishing  the  cervical  enamel  margin. 
Different  sizes  result  through  wear.  The  other  forms  of  these 
points  (Fig.  88)  may  sometimes  be  required.    The  small  car- 


70 

borunduni  disk  (j^ig.  89),  as  well  as  the  stone  shown  in  Fig.  116, 
is  used  to  cut  out  the  fissures  on  the  occlusal  surface, 
and  to  prepare  cavities  for  the  dove-tail  or  the  hook  an- 
chorage. 

If  the  smallest  diameter  of  a  cavity  is  less  than  an  ^'g  inch, 
stones  cannot  be  used.  The  caA^ity  must  then  be  prepared 
with  burs,  and  the  margins  finished  with  plug  finishing  burs, 
or  in  a  manner  to  be  described  later. 

As  a  substitute  for  small  stones,  instruments  impregnated 
with  diamond  dust  have  been  put  upon  the  market.  Owing 
to  their  high  price  and  their  rapid  deterioration,  they  have 
not  come  into  general  use.  Instruments  made  of  copper  and 
used  with  carborundum  powder  are  more  satisfactory.  It  will 
be  found,  however,  that  aluminum  cuts  still  better.  Small 
disks  cut  out  of  aluminum  plate,  are  mounted  on  a  man- 
dril and  trued  on  the  engine.  A  cylindrical  form  is  made 
bv  cementing  a  short  piece  of  small,  thick- walled  aluminum 
tubing  upon  an  old  bur,  and  trueing  as  described  above. 
As  a  cutting  medium,  coarse  carborundum  powder,  mixed 
to  a  stiff  mass  with  low -melting  paraffin,  can  be  recom- 
mended. In  grinding  it  becomes  less  fluid  than  vaseline  and 
is  therefore  not  thrown  off  of  the  disk  as  easily.  A  small 
piece  of  the  mass  is  placed  in  the  cavity.  The  heat  generated 
in  cutting  sufficiently  Hquifies  the  paraffin  to  insure  a  constant 
supply  of  carborundum  powder  at  the  cutting  edge.  If  the 
mass  is  too  hard,  the  instrument  should  first  be  dipped  into 
vasehne.  During  the  operation,  it  is  advisable  to  cool  the 
tooth  with  air.  In  cutting  with  abrasive  powders,  pressure 
should  never  be  applied  to  the  instrument. 

Cavities  cut  by  this  process  have  extremly  smooth  walls 
and  almost  knife-edged  margins.  It  will  never  be  generally 
adopted,  however,  unless  diamond- dust,  real  or  artificial,  can 
be  produced  so  cheaply  as  to  replace  the  carborundum  powder. 
In  that  case  it  would  be  a  most  rapid  and  painless  method 
of  excavating  cavities.  The  great  disadvantage  in  its  present 
form  is,  that  in  comparison  to  the  cutting  speed  of  carborundum 
stones  and  steel  burs,  it  is  very  slow.  In  small  cavities,  pre- 
pared with  burs,  a  very  smooth  enamel  margin  can  be  obtained 


71 


more   rapidly   with  carborundum-powder  and  aluminum  than 
with  arkansas -stones. 

The   right-angle   hand-piece   is  indispensable  in  the  pre- 
paration of  cavities  for  inlays.    In  other  methods  of  filling, 


'^^ 


Fig.  90. 


Fk.  01. 


the  cavities  can  be  prepared  with  the  straight  hand-piece. 
The  inlay,  however,  requires  a  cavity  perfectly  free  from  under- 
cuts, and  this  can  be  produced  only  by  working  in  the  direction 
in  which  the  impression  is  to  be  removed  from  the  cavity. 
The  cutting  instrument  must  therefore  in  each  case  occupy 


72, 


Fig.  92. 


a  certain  definite  position.  This  can  be  accom- 
plished, as  a  rule,  only  by  the  use  of  the  right- 
angle  hand-piece. 

The  general  prejudice  against  this  instrument 
is  the  result  of  the  incorrect  form  of  most  right- 
angle  hand-pieces.  Usually  the  head  of  the  bur  lies 
far  from  the  axis  of  the  hand-piece,  thus  making 
accurate  work  impossible.  In  the  contra- angle 
(Fig.  90)  this  deficiency  has  been  remedied  to  a 
great  extent.  The  head  of  the  bur  lies  about  in 
the  axis  of  the  hand -piece,  thereby  giving  the 
operator  almost  the  same  control  over  the  cutting 
instrument  as  in  a  straight  hand-piece.  Even  in 
the  contra-angle  the  tips  of  the  long  cylindrical 
stones  do  not  lie  quite  in  the  axis.  This  is  rarely 
disturbing  unless  the  stones  are  too  long. 

In  selecting  a  right -angle  for  inlay  cavity 
preparation,  it  must  be  ascertained  that  the  head 
of  the  ordinary  bur  lies  in  the  axis  of  the  hand- 
piece, and  that  the  distance  from  the  angle  of  the 
shank  to  the  head  is  sufficiently  long.  If  this 
distance  is  too  short  (Fig.  91,  a)  the  angle  in  the 
shank  must  be  more  acute  in  order  to  bring  the 
head  of  the  bur  into  the  axis  of  the  hand-piece. 
This  places  the  axis  of  the  bur  in  an  unfavorable 
position;  considerably  less  than  at  a  right-angle 
to  the  axis  of  the  hand-piece.  As  the  cutting 
instrument  must  always  be  applied  at  right-angles 
to  the  surface  of  the  tooth,  a  hand-piece  of  this 
form  is  almost  useless  in  preparing  cavities  for  in- 
lays in  the  posterior  teeth. 

The  use  of  stones  causes  the  hand-pieces  to  wear 
out  very  quickly,  owing  to  water  mixed  with 
carborundum  being  drawn  up  along  the  mandril. 
The  right-angle  suffers  most  in  this  respect.  The 
straight  hand -piece  can  be  protected  from  this 
injury,  which  is  especially  marked  in  working  upon 
the   upper  teeth,   by  using  Kief er's  aseptic  rubber 


73 

sheaths  (Fig.  92).  The  mandril  should  be  coated  with  vaseline 
before  introduction  into  the  hand-piece.  Though  making  a  mois- 
ture-proof joint,  the  objection  to  the  use  of  these  sheaths  is 
the  difficulty  of  stretching  them  over  the  hand-piece.  As,  for 
reasons  of  asepsis,  a  fresh  sheath  should  be  used  for  each 
patient,  their  use  entails  considerable  trouble.  If  a  small 
rubber  cap  of  this  style  could  be  made,  to  easily  slip  over 
the  head  of  the  right-angle,  it  would  greatly  prolong  the 
usefulness  of  this  hand-piece.  The  instruments  necessary  in 
finishing  and  polishing  the  inlay,  will  be  described  in  a  later 
chapter. 


Chapter  VIII. 
Cavity  Preparation. 

A  description  of  each  and  every  cavity  which  could  be 
filled  with  an  inlay,  would  be  of  little  use  to  any  one  not 
acquainted  with  the  fundamental  principles  of  the  cavity- 
forms  for  inlays  (Chap.  Ill  and  IV).  The  operator  who  fully 
understands  these  principles  has  no  need  to  follow  a  descrip- 
tion or  an  illustration  in  preparing  a  cavity.  He  is  able  to 
decide  in  each  case,  what  form  of  cavity,  and  which  anchorage 
is  most  suitable.  The  description  of  cavities  will  therefore 
be  limited  to  those  generally  filled  with  inlays,  and  the  chief 
points  to  be  considered  in  the  preparation,  will  be  only  briefly 
mentioned. 

As  a  rule  the  cavity  must  be  opened  with  chisels  or  burs, 
before  stones  can  be  used.  When  the  opening  is  sufficiently 
large  a  stone  of  suitable  form  is  employed.  Care  should  be 
exercised  in  the  selection  of  the  stone,  as  with  one  of  proper 
shape  the  correct  cavity- form  is  cut  almost  autoraatically. 
Leathery  dentine  must  first  be  removed  with  excavators,  as 
stones  cut  it  but  slowly. 

The  cavity  is  prepared  until  it  presents  a  margin  of  healthy 
dentine  and  enamel.  Carious  spots,  not  near  the  margin  are 
removed  after  the  impression  has  been  taken.  It  sometimes 
occurs,  that  the  general  form  and  the  margin  are  satisfactory 
while  there  still  are  undercuts  in  the  walls  of  the  cavity. 
In  such  cases  the  latter  should  be  filled  with  Fletcher's  Artificial 
Dentine,  and  the  cavity  again  ground  out  with  stones  of 
suitable  form. 

Where  there  is  danger  of  injuring  the  neighboring  tooth, 
stones  of  small  diameter  should  be  used.  If  contact  is  un- 
avoidable, placing  a  piece  of  a  thin  seperating  file  in  the 


75 

interproximal  space,  is  to  be  recommended.  When  worn 
through  a  new  piece  is  substituted.  This  precaution  is,  how- 
ever, rarely  necessary. 

The  following  plates  are  reproductions  of  cavities  cut  into 
enlarged  plaster  models  of  teeth.  In  the  mouth  where  the 
conditions,  especially  in  regard  to  accessibility,  are  not  so 
favorable,  it  is  not  always  possible  to  prepare  the  cavities 
so  exactly.    This  is  true  particularly  of  the  enamel  margin. 


76 


Plate  I. 
Lower  Molar  with  Mesio- Occlusal  Cavity. 

The  proximal  cavity  should  be  broad,  and  be  prepared 
with  care  in  the  region  of  the  pulpal  horns.  These  points  of 
danger  lie  upon  a  line  drawn  from  the  tips  of  the  cusps  to 
the  pulp-chamber  (Fig.  81).  Between  the  pulpal  horns,  the 
cavity  has  been  deepened,  to  make  the  segment  {d,  Figs.  49 
and  53)  as  strong  as  possible.  The  enamel  margin  is  to  be 
bevelled  as  described. 

On  the  occlusal  surface,  the  fissures  have  been  cut  out  with 
a  carborundum  disk.  The  sharp  angles  produced  at  the  cross- 
ing of  the  fissures  have  been  rounded.  If  the  excavated 
fissure  extends  to  the  edge  of  the  occlusal  surface,  the  margin 
of  the  enamel  should  be  ground  away  horizontally.  (On 
plate  I,  the  left  end  of  the  transverse  fissure.)  At  other  points 
of  the  occlusal  cavity,  bevelling  the  enamel  margins  is  not 
necessary  if  deep  fissures  are  carved  in  the  inlay. 


Plate  I. 


Plate  II. 


77 


Plate   II. 

Lower  Molar  with  Disto -Proximal  Cavity. 
Adjoining  Tooth  Missing. 

The  presence  of  a  filling  upon  the  occlusal  surface  is 
assumed.  The  adjoining  tooth  being  absent  and  the  occlusal 
surface  but  slightly  involved,  the  inlay  may  be  made  without 
self-retention.  The  greater  part  of  the  proximal  surface  being 
carious,  the  cavity  could  not  be  prepared  like  Fig.  54.  Suffi- 
cient retention  has  been  obtained  by  cutting  all  the  walls, 
at  right- angles  to  the  proximal  surface.  The  enamel  margins 
have  been  bevelled.  On  the  inlay,  the  small  occlusal  surface 
should  be  sloped  proximally  (Fig.  16). 


78 


Plate  III. 
Lower  Molar  with  Lingual  Wall  Missing. 

To  seat  the  inlay  more  firmly,  the  gutta-percha  filling 
the  pulp-chamber  has  been  partially  removed,  and  the  remain- 
ing portion  of  the  lingual  wall  ground  off  horizontally.  The 
enamel  margins  have  been  bevelled,  with  the  exception  of 
those  of  the  dove-tail  anchorage  cavity.  For  the  preparation 
of  the  latter  see  Figs.  27  and  28. 


Plate   III. 


Plate  IV. 


79 


Plate  IV. 
Lower  Molar  with  Abraded  Occlusal  Surface. 

The  cavity  should  be  made  as  broad  and  deep  as  possible; 
the  walls  cut  vertically  and  their  upper  edges  rounded.  To 
give  greater  security  against  dislocation,  the  grooves  instead 
of  being  cut  obliquely,  may  extend  entirely  through  the  walls 
of  the  cavity.  If  necessary,  the  pin  anchorage  (Fig.  32)  may 
be  used.    The  enamel  margins  are  to  be  broadly  bevelled. 


80 


Plate  V. 
Lower  Bicuspid  in  a  Crowded  Arch,  with  Mesio- Occlusal  Cavity. 

The  mesial  surface  of  the  tooth  has  been  flattened  with 
a  diamond  disk.  The  margin  of  the  enamel  in  this  case  should 
not  be  bevelled.  Retention  is  obtained  by  means  of  a  strong 
fissure  anchorage,  or  if  preferred  by  cutting  a  dove-tail  in 
the  distal  part  of  the  occlusal  surface.     (See  page  60.) 


Plate  V. 


Plate  VI. 


81 


Plate  VI. 

Upper  Bicuspid  with  Large  Mesial  and  Distal  Cavities 
(Tooth  Pulpless). 

The  cavities  are  prepared  in  the  usual  manner,  and  the 
margin  of  the  enamel  bevelled.  To  prevent  a  subsequent 
fracture  of  the  lingual  or  buccal  wall,  the  inlay  should  com- 
pletely cover  the  occlusal  surface.  The  gold  should  have  the 
greatest  possible  thickness  and  at  the  same  time  be  invisible 
in  the  mouth.  To  accomplish  this,  the  occlusal  surface  is 
bevelled  lingually  and  bucally  from  the  tips  of  the  cusps 
toward  the  fissure  with  a  diamond-disk. 


Bo  decker,  Metallic  Inlay. 


82 


Plate  VII. 
Upper  Bicuspid  with  Lingual  Wall  Missing. 

As  the  form  of  this  tooth  offers  no  broad  seat  for  the 
inlay  (as  in  plate  III),  a  pin  must  usually  be  inserted.  This 
should  be  placed  as  far  lingually  as  possible.  Its  length  is 
dependent  upon  the  strength  of  the  wall  still  standing.  Proxi- 
mally  the  enamel  margin  is  bevelled  slightly,  while  cervically 
it  is  broadly  bevelled,  especially  at  the  lingual  margin.  The 
occlusal  surface  of  the  buccal  wall  is  bevelled  lingually.  To 
make  the  gold  invisible  in  the  mouth,  the  hook  retention 
should  be  cut  into  the  distal  margin,  behind  the  cusp.  If  the 
wall  is  weak,  a  second  hook  retention  mesially  is  necessary. 
In  the  preparation,  special  care  should  be  exercised  to  make 
the  wall  {a,  Fig.  25)  on  the  buccal  surface  vertical,  and  suffi- 
ciently large. 


Plate  VII. 


Plate  VIII. 


83 


Plate  VIII. 

Upper  Bicuspid  with  Buccal  Wall  Missing. 

The  remaining  buccal  portion  of  the  tooth  is  ground  off 
to  the  margin  of  the  gum,  and  if  possible,  the  edge  bevelled 
buccally.  The  lingual  cusp  is  removed  and  the  surface  sloped 
lingually.  The  margins  of  this  surface  are  all  broadly  bevelled. 
The  post,  which  should  be  long  and  strong,  is  placed  into  the 
canal,  and  an  impression  taken  with  a  thin  copper  ring  and 
modelling  compound.  The  model  is  poured  in  Spence-metal. 
Upon  this  model,  the  porcelain  facing  selected  is  ground  up. 
To  permit  the  removal  of  the  facing  during  casting,  the  pins 
are  covered  with  moldine,  and  the  facing  well  oiled.  Upon 
-the  Spence  model,  the  wax  form,  with  post  and  facing  in 
position  but  without  an  occlusal  surface,  is  carved.  This  is 
then  tried  in  the  month,  and  after  the  position  of  the  facing 
has  been  corrected  and  the  margins  smoothed,  the  wax  is 
chilled.  To  prevent  distortion  at  this  stage,  there  should  not 
be  sufficient  wax  on  the  occlusal  surface  to  come  in  contact 
with  the  antagonist.  The  form,  having  been  thoroughly  chilled, 
is  removed  from  the  mouth,  dried,  soft  wax  added  upon  the 
occlusal  surface,  and  again  placed  in  the  tooth,  and  the  patient 
requested  to  close  quickly.  By  alternately  chilling  the  form 
with  cold  water  and  softening  the  surface  with  hot  air,  a  per- 
fect articulation  can  be  carved  without  disturbing  the  lower 
parts  of  the  wax  form  previously  completed.  To  prevent 
distortion  of  the  wax,  the  post  is  firmly  held  in  a  pin-vise 
and  the  facing  removed  by  the  aid  of  a  rod  of  sticky  wax. 
The  form  is  then  cast,  and  the  facing  attached  with  cement. 
If  but  little  of  the  lingual  wall  remains  and  the  bite  is  favo- 
rable, regular  porcelain  teeth  with  occlusal  surfaces  can  be  used. 


84 


Plate  IX. 
Upper  Bicuspid  with  Erosion. 

If  the  margins  of  the  defect  are  sharply  naarked,  two  semi- 
circular steps  are  cut  at  right- angles  to  the  surface  of  the 
tooth  with  a  large  fissur  bur.  The  curved  surfaces  of  these 
steps  should  lie  opposite  one  another  and  be  parallel  to  the 
direction  in  which  the  inlay  can  be  removed  from  the  cavity. 
At  these  points  regular  undercuts  (Fig.  10)  should  be  made 
in  the  tooth  and  in  the  inlay.  If  the  margins  of  the  defect 
are  not  sharply  marked,  they  can  easily  be  made  so  with  a 
diamond  disk. 

Upper  Bis  cuspid  with  Simple  Cervical  Cavity. 

The  upper  and  lower  wall  are  to  be  made  parallel  and 
the  margins  bevelled  (Fig.  39). 


Plate  IX. 


Plate  X. 


85 


Plate  X. 
Cuspid  with  Small  Distal  Cavity. 

The  cavity  should  be  prepared  almost  at  right-angles  to 
the  lingual  surface  of  the  tooth.  The  margin  is  to  be  care- 
fully bevelled.  The  labial  groove  is  prepared  vertically,  the 
lingual,  as  horizontally  as  possible. 


86 


Plate  XI. 
Cuspid  with  Large  Distal  Cavity. 

The  distal  angle  of  the  tooth  is  removed  with  a  disk.  The 
labial  surface  is  so  cut  out,  that  the  walls  of  this  part  of  the 
cavity  lie  parallel  to  the  long  axis  of  the  tooth.  (In  the  illus- 
tration this  part  has  been  cut  out  more  broadly  than  necessary.) 
The  labial  groove  should  lie  vertically  and  the  lingual  groove 
horizontally.  The  margin  of  the  enamel  should  be  bevelled 
only  between  the  two  grooves  and  in  the  region  of  the  lingual 
cusp. 


Plate  XI. 


Plate  XII. 


87 


Plate  XII. 
Abraded  Cuspid,  with  Inlay  Anchored  on  the  Lingual  Surface. 

This  form  of  retention  is  used  chiefly  in  cuspids  and  in- 
cisors with  marked  lingual  abrasion.  The  incisive  edge  is 
ground  off  horizontally  and  the  enamel  margin  bevelled.  In 
the  lingual  surface  of  the  tooth,  a  shallow  cavity  is  cut,  extend- 
ing almost  to  the  margin  of  the  gum.  Care  should  be  taken 
to  make  the  lingual  wall  vertical  and  as  large  as  possible, 
as  the  retention  of  the  inlay  depends  chiefly  upon  this  wall 
of  the  cavity.  On  the  lingual  margin  the  enamel  should  be 
carefully  bevelled. 

Incisor  with  Small  Proximal  Cavity. 

A  metal  inlay  would  not  be  indicated  in  a  cavity  of  this 
kind.  If,  however,  such  a  case  should  occur,  the  cavity  could 
be  prepared  in  a  form  recommended  for  porcelain  inlays. 


Plate  XIII. 
Incisor  with  Mesial  and  Distal  Cavities. 

In  cases  of  this  kind  also,  a  metal  inlay  would  hardly 
ever  be  indicated.  At  most,  a  combination  inlay  could  be 
recommended,  as  the  smaller  cavity  offers  sufficient  hold  to 
allow  the  larger  one  to  be  filled  partially  with  porcelain. 
(Figs.  102 — 104).  The  enamel  margins  should  be  but  slightly 
bevelled,  so  as  not  to  interfere  with  the  removal  of  the  im- 
pression. 


Plate  XIII. 


Plate   XIV. 


89 


Plate  XIV. 
Abraded  Incisor  with  Mesial  and  Distal  Cavities. 

Such  cases  are  suitable  for  gold  inlays,  especially  if  the 
bite  is  strong.  The  incisive  edge  is  bevelled  labially  and  the 
proximal  cavities  so  prepared  that  the  impression  can  be 
removed  easily.  The  final  form  of  such  a  double  cavities  is 
dependent  upon  the  extent  of  the  caries  upon  the  proximal 
surfaces,  and  will  therefore  vary  with  each  case.  The  margins 
of  the  enamel  should  be  carefully  bevelled. 

If  the  tooth  is  considerably  abraded  horizontally,  and  there 
is  no  caries  on  the  proximal  surfaces,  the  cavity  for  the  inlay 
may  be  prepared  in  the  box-shaped  manner  recommended  for 
cohesive  gold  fillings*),  with  or  without  the  pin-anchorage, 
as  the  case  may  require. 


*)  L.  Warnekros,  Das  Fiillen  cler  Zahne  bei  intakter  Pulpa  (Ash  &  Sons  1888). 


Chapter  IX. 
The  Impression. 

The  wax-model  of  an  inlay  may  be  made  in  two  ways, 
either  an  impression  of  the  cavity  is  taken  in  modeling  com- 
pound and  a  cement  model  made  upon  which  the  wax  form 
is  built  up,  or  the  wax  model  is  made  directly  in  the  cavity 
of  the  tooth.  Strictly  speaking,  the  wax-model,  in  each  case, 
represents  an  impression  of  the  cavity.  The  form  made  in 
the  mouth  may  be  called  a  direct  impression,  while  that  made 
on  a  model  may  be  referred  to  as  an  indirect  impression. 

The  indirect  impression. 

Since  the  first  gold  inlays  were  made,  this  method  of 
taking  impressions  has  been  in  use.  Though  the  models  at 
first  were  not  very  perfect,  improvements  in  the  methods, 
as  well  as  of  the  impression  compounds,  have  led  to  satis- 
factory results. 

The  impression  compound  should  be  made  up  in  the 
form  of  cones  and  rods  of  different  sizes.  The  impression  of 
a  simple  cavity  is  taken  with  a  rod-shaped  piece  of  com- 
pound whose  diameter  is  slightly  greater  than  that  of  the 
cavity.  The  piece  should  be  only  about  an  inch  in  length, 
as  otherwise  it  tips  easily  under  pressure  and  gives  a  double 
impression  of  the  margin.  Only  the  tip  of  the  rod  is  softened 
over  an  alcohol- flame,  and  the  compound  then  pressed  into  the 
cavity  at  right-angles  to  the  surface  of  the  tooth.  If  the 
cavity  is  situated  at  the  neck  of  the  tooth,  the  harder  material 
presses  away  the  gum,  thereby  giving  a  perfect  impression  of 
the  margins. 

Cavities  not  possessing  four  walls,  require  some  appliance 
to  prevent  the  escape  of  impression  material.  Of  these  the 
most  commonly  used  are  thin  copper  rings.   A  supply  of  such 


91 

rings  of  all  required  sizes,  should  alway  be  kept  on  hand. 
In  all  larger  cavities,  unless  the  direction  in  which  the  im- 
pression may  be  removed  from  the  cavity  prevents,  the  copper 
ring  is  of  the  greatest  service.  If  the  form  of  the  tooth  or  the 
position  of  the  cavity  makes  the  use  of  the  ring  impracticable, 
other  means  must  be  employed  to  prevent  the  escape  of  the 
impression  material.  Without  describing  the  numerous  appli- 
ances, it  may  be  stated  that  they  are  all  more  or  less  modified 
matrices,  similar  to  those  used  in  making  gold  or  amalgam 
fillings.  Impression-trays  or  other  appliances  with  long  handles 
cannot  be  recommended.  The  almost  inevitable  lateral  move- 
ment while  pressing  the  material  into  the  cavity  and  while 
holding  it  in  this  position  until  it  has  set,  makes  a  double, 
or  a  distorted  impression  almost  unavoidable. 

The  model  may  be  made  of  one  of  the  following  materials: 
hard  plaster,   cement,   amalgam,    Spence  or  Melotte's  metal. 

The  plaster  model  is  the  easiest  to  make,  but  has  the 
disadvantage  that  if  ordinary  plaster  is  used,  thin  walls  are 
liable  to  break  off.  With  but  little  care  in  carving  the  wax 
form,  a  model  made  of  the  so-called  alabaster  plaster  will  do 
good  service.  This  material  is  considerably  harder  than 
ordinary  plaster,  and  sets,  if  salt  has  been  added,  in  about 
half  an  hour.  The  hardest  of  all  varieties  of  plaster,  the  so- 
called  marble-plaster,  has  the  disadvantage  that  it  sets  com- 
pletely only  in  about  twelve  to  sixteen  hours.  It  then  furnishes 
a  model,  equally  as  good  as  one  made  of  cement  or  amalgam. 

If  the  model  is  to  be  made  of  cement  or  of  amalgam,  the 
impression  should  be  so  imbedded  in  plaster,  that  it  cannot 
be  fractured  by  the  force  exerted  in  introducing  the  material. 
The  cement  need  not  possess  great  edge- strength,  as  it  is  not 
subjected  to  the  high  pressure  formerly  used  in  swedging  the 
matrices  for  gold  inlays.  The  cement  for  the  model  is  mixed 
so  that  it  is  just  kneadable,  without  sticking  to  the  fingers. 
The  mass  is  firmly  pressed  into  the  oiled  impression,  and  the 
surplus  formed  under  pressure,  between  the  thumbs  and  index 
fingers,  into  a  small  pyramid.  After  the  cement  has  set,  in 
fifteen  to  sixty  minutes  according  to  the  preparation  used,  the 
impression  is  removed  and  the  model  cleaned  with  chloroform. 


92 

Copper  amalgam  is  the  variety  m.ost  commonly  employed 
for  models,  as  it  may,  by  simply  heating,  be  repealedly  used. 
The  preparation  of  the  impression  and  the  introduction  of 
the  material  are  the  same  as  have  been  described  for  cement. 
The  slowness  in  setting  is  the  chief  disadvantage  of  the  amalgam 
model. 

In  making  the  model  of  Spence  or  Melotte's  metal,  the 
impression  is  embedded  in  Moldine  surrounded  with  a  ring, 
and  cast  under  the  usual  precautions.  By  this  method,  in  but 
a  few  minutes  the  finished  model  may  be  produced.  With 
a  good  Spence  metal,  for  example  the  White  Inlay  Metal,  to 
which  flowers  of  sulphur  are  occasionally  added,  the  model 
presents  smooth  surfaces  and  sharp  margins. 

Upon  the  previously  oiled  model  of  the  cavity,  the  wax 
form  is  carved.  It  is  always  advisable  to  try  the  wax  form 
in  the  mouth  before  casting,  in  order  to  control  the  correct- 
ness of  the  bite,  the  contact  point,  and  the  margins.  If  the 
form  cannot  be  tried  in  the  mouth,  the  following  method  must 
be  employed.  After  the  impression  of  the  cavity  has  been 
taken,  a  piece  of  fairly  hard  modelling  compound,  about  the 
size  of  a  hayel-nut  is  placed  upon  the  cavity  and  the  patient 
requested  to  occlude.  The  result  is  an  impression  of  the  margins 
of  the  cavity,  the  proximal  surfaces  of  the  adjoining  teeth,  and 
the  occlusal  surface  of  the  antagonist.  The  model  of  the  cavity 
is  then  placed  in  this  impression  so,  that  the  margins  of  the 
cavity  on  the  model  and  those  in  the  impression  exactly 
correspond.  After  attaching  the  cavity  model  to  the  im- 
pression with  wax,  the  model  of  the  bite  is  poured  in  plaster, 
in  two  parts.  If  the  bite  has  been  taken  carefully,  and  the 
model  of  the  cavity  placed  exactly  in  the  bite  impression, 
a  true  reproduction  of  the  conditions  in  the  mouth  will  be 
obtained.  In  spite  of  the  greatest  care,  this  method  does  not 
give  as  good  results,  as  trying  the  wax  form,  previously  carved 
on  a  model,  in  the  mouth. 

The  direct  impression. 

Until  lately,  this  method  of  taking  an  impression  has  not 
received  the  recognition  of  which  it  is  worthy.    It  represents 


93 

in  the  field  of  metallic  inlay  technic,  an  advance,  equal  almost 
to  the  introduction  of  casting.  It  was  necessary  in  the  old 
swedged  and  soldered  inlays  to  construct  the  form  in  three 
stages.  First  the  impression  in  the  mouth,  then  the  cement 
model,  and  lastly  the  swedged  matrix.  Each  of  these  stages 
represents  a  source  of  error  for  the  perfect  fit  of  the  inlay. 
The  introduction  of  casting,  obviated  the  necessity  of  making 
a  matrix,  and  it  soon  became  evident  by  the  better  adaptation 
of  the  inlays,  that  one  source  of  error  at  least,  had  been 
partially  removed.  Only  partially,  however,  as  the  form  must 
still,  as  in  the  indirect  impression,  pass  through  three  stages. 
But  the  error  with  easily  adaptable  wax  is  far  less  than  that 
with  the  stiff  platinum  matrix.  Experience  in  the  arts  has 
shown,  that  in  a  series  of  models,  each  reproduced  from  the 
previous  one,  the  form  of  the  original  becomes  more  altered 
with  each  subsequent  model.  Applied  to  the  inlay  process, 
it  becomes  evident  that  if  the  intermediary  stages  could  be 
avoided,  that  is,  the  wax  form  made  directly,  without  com- 
pound impression  or  model,  a  decided  advantage  for  the  inlay 
would  be  gained.  In  theory  the  method  of  making  direct  im- 
pressions rest  upon  a  logical  basis.  In  practice,  the  difficulties 
at  first  met  with  are  due  to  inexperience  and  to  the  use  of 
unsuitable  instruments.  Carving  a  wax  form  in  the  mouth 
requires  the  same  care  as  making  a  cement  or  gutta-percha 
filling.  As  most  operators  have  had  no  experience  in  the  use 
of  wax  as  a  filling -material,  its  manipulation  must  first 
be  learned.  With  patience  and  practice  this  is  readily  accom- 
plished. 

Before  describing  the  process  of  taking  a  direct  impression, 
a  few  words  upon  the  qualities  of  the  wax  used  for  this  pur- 
pose are  necessary.  Pure  bees-wax  cannot  be  used,  as  it  is 
too  soft  and  tough  to  carve  well.  Other  substances  must 
therefore  be  added  to  make  it  harder  and  more  workable, 
as  well  as,  to  give  it  the  other  necessary  qualities. 

In  making  the  form  in  the  mouth,  the  hardness  of  the  wax 
is  of  great  importance.  This  being  dependent  upon  temperature 
and  the  quantity  of  resins  etc.  added,  a  wax  can  be  produced, 
that  at   100  °  F  will  change  its  form  only  under  considerable 


94 

pressure.  For  the  hardening  point  of  the  wax,  100  °  F  is  about 
the  most  favorable  temperature,  as  this  is  several  degrees  above 
that  of  the  teeth  when  the  mouth  has  been  opened  for  a  short 
time.  If  the  hardening-point  is  below  this,  the  wax  remains 
soft  in  the  mouth,  and  the  form  is  very  liable  to  be  distorted 
during  removal  from  the  cavity.  For  the  same  reason,  the 
form  cannot  be  easily  handled  outside  of  the  mouth,  nor 
can  it  be  carved  while  being  held  between  the  fingers.  If  the 
hardening-point  is  much  above  100°  F,  the  wax  becomes  brittle, 
and  weaker  processes  and  extensions  are  liable  to  break  off 
even  before  the  wax  form  can  be  removed  from  the  cavity. 

Intimately  connected  with  the  hardening  of  the  wax,  is 
its  power  of  recovery.  If  two  varieties  of  wax,  both  hardening 
at  80  °  F,  are  slowly  heated  until  they  begin  to  soften,  and 
are  then  placed  in  water  of  80  °  F,  a  marked  difference  in  the 
time  required  for  each  variety  to  harden,  and  to  regain  its 
other  qualities  will  be  found.  The  inlay  technic  requires  a 
wax  with  rapid  recovery. 

More  or  less  related  to  the  hardness  of  the  wax,  is  the 
ease  with  which  it  can  be  scraped.  A  soft  wax  cannot  be 
scraped,  it  can  only  be  cut.  This  in  an  inlay-wax  is  not  per- 
missible, as  in  cutting  the  tough  mass,  the  form  would  un- 
doubtedly become  distorted.  Yet  not  every  hard  wax  is 
suitable,  as  many  of  these  also  are  tough.  To  test  the  scraping 
quality,  the  wax  should  be  scraped  at  room  temperature  with 
a  sharp  instrument.  The  surface  should  be  clear  and  smooth, 
and  the  scrapings  be  of  a  fine  grain.  Rubbed  on  the  palm 
of  the  hand,  they  should  not  ball,  but  remain  as  small  par- 
ticles. The  wax  should  not  rapidly  clog  the  grit  of  a  sand- 
paper strip. 

Another  quality  possessed  by  a  good  inlay  wax,  is  cohesion 
at  comparatively  low  temperature.  This  permits  the  wax 
being  formed  by  hand,  in  each  case  so,  that  the  bottom  or 
the  cervical  margin  of  the  cavity  may  with  certainty  be 
reached.  Folds  produced  by  the  introduction  of  the  wax  into 
the  cavity  will  disappear  under  pressure,  thus  making  the 
model  a  perfectly  homogeneous  mass.  Another  advantage 
that  a  wax  with  marked  cohesion  at  low  temperature  offers, 


95 

is  that  fresh  wax  may  be  added  outside  of  the  mouth,  without 
danger  of  distorting  the  form  through  heat. 

Under  no  circumstances  should  the  wax  be  adhesive. 
Adhering  to  the  instrument,  it  would  make  scraping  im- 
possible. It  would  also  prevent  the  easy  removal  of  the  model 
from  the  cavity. 

The  wax  should  be  sufficiently  dark  in  color  to  readily 
show  where  it  extends  beyond  the  margin  of  the  cavity.  It 
should  however  not  be  so  dark,  that  it  is  impossible  to  re- 
cognize the  cavity  margin  through  a  thin  layer.  The  coloring 
matter  must  contain  no  metal,  as  this  would  be  deposited  on 
the  walls  of  the  casting  form  when  the  wax  is  burned  out, 
and  thereby  affect  the  surface  of  the  inlay. 

Convinced  of  the  great  value  of  the  direct  impression 
method,  the  writer  performed  a  number  of  experiments,  to 
determine  the  possibility  of  producing  a  wax  having  all  the 
qualities  described  above.  In  how  far  he  has  suceeded,  he 
leaves  the  profession  to  decide  for  itself. 

Equal  in  importance  to  a  good  wax,  are  proper  instru- 
ments. Even  the  most  skilful  operator  is  not  able  to  pro- 
duce a  perfect  wax  model  in  the  mouth  without  suitable 
instruments.  It  is  not  the  intention  of  the  writer  to  describe 
a  complete  set  of  instruments,  sufficient  for  every  case.  Only 
a  few,  found  to  be  of  service  will  be  mentioned.  In  all  these 
instruments,  the  cutting  edges  should  be  as  sharp  as  possible, 
so  that  the  wax  may  be  scraped  without  the  exertion  of 
pressure. 

As  a  spatula  the  instrument  shown  in  No.  1  (Fig.  93)  may 
be  used.  To  remove  the  excess  upon  the  occlusal  surface 
a  spoon-shaped  excavator,  about  a  quarter  of  an  inch  in  dia- 
meter is  of  service  (No.  2).  A  smaller  spoon  (No.  3)  is  ne- 
cessary to  deepen  the  impressions  made  by  the  cusps  of  the 
antagonist.  In  carving  the  fissures,  the  instrument  shown 
in  No.  4  is  used.  This  is  a  Darby-Perry  excavator  No.  3,  the 
tip  of  which  has  been  ground  to  a  point.  The  angle  made  by 
the  two  cutting  edges  represents  about  the  form  of  a  fissure 
of  a  natural  tooth.  In  modeUing  the  proximal  surface,  the 
last  three  instruments  are  of  service.    For  the  coarser  work. 


96 

a  curved  cement  spatula  (No.  5),  and  the  spatulate  end  of 
a  Woodson's  amalgam  instrument  (No.  7).  To  model  the  less 
accessible  cervical  margin,  the  writer  uses,  the  instrument 
No.  6.  This  is  made  by  grinding  a  right-angled  exploring 
instrument  so,  that  in  cross  section  it  appears  as  a  triangle. 
One  side  of  the  triangle  should  face  the  handle  of  the  in- 
strument.   In  scraping,  the  point  is  pressed  against  the  neck 


Fiff.  93. 


of  the  tooth,  and  all  material  overlapping  the  cervical  margin 
thereby  smoothly  removed.  In  the  same  manner  this  instru- 
ment may  be  used  to  trim  the  other  margins  on  the  proximal 
surface.  Beside  the  instruments  mentioned,  sand-paper  or 
cloth  strips  are  employed  in  modelling  the  wax  in  the  mouth. 
Every  operator,  in  time,  develops  his  own  method  of 
taking  a  direct  impression.  The  following  description  is,  there- 
fore, intended  only  as  a  suggestion.  Oiling  the  cavity  is  to 
be  avoided,  as  a  good  inlay- wax  is  not  adhesive.  Before  intro- 
ducing the  wax,  the  cavity  is  rinsed  out  with  water.  In  ex- 
ceptional cases  cotton  rolls  are  used  to  keep  the  field  of  opera- 


97 

tion  dry.  As  this  makes  carving  easier,  it  may  be  recommended 
to  those  trying  this  method  for  the  first  time. 

The  stick  of  wax  is  warmed  slowly  over  an  alcohol  flame 
until  it  is  so  soft  that  a  piece  can  be  pinched  off  with  the  fingers, 
and  kneaded.  In  warming,  the  surface  of  the  wax  should  not 
be  overheated,  as  this  affects  its  power  of  recovery  and  its 
scraping  qualities.  The  same  is  true  of  a  prolonged  kneading 
of  the  wax. 

As  an  example,  the  disto-occlusal  cavity  of  a  lower  molar 
has  been  chosen.  If  the  interproximal  space  is  large  or  un- 
favorable in  form,  as  in  the  lower  bicuspids,  a  matrix  lightly 
held  in  position  with  cotton,  is  of  advantage.  The  softened 
wax  is  formed  into  a  cone,  sufficiently  slender  to  reach  the 
bottom  of  the  cavity.  The  surface  of  the  cone  is  again  softened 
in  the  flame  and  quickly  introduced.  With  the  index- finger 
firm  downward  pressure  is  brought  to  bear  on  the  wax,  until 
the  proximal  cavity  is  filled,  then  by  drawing  the  finger  for- 
ward under  pressure,  the  excess  wax  is  forced  into  the  cavity 
on  the  occlusal  surface.  The  patient  is  requested  to  occlude, 
and  to  keep  the  teeth  together  tightly  at  least  thirty  seconds, 
to  allow  the  wax  sufficient  time  to  escape.  In  case  the  bite 
is  very  sharp,  a  small  piece  of  thick  rubber-dam  should  be 
laid  over  the  wax  before  closure  of  the  teeth.  The  danger 
of  making  the  inlay  too  high,  is  thereby  partially  avoided. 

The  excess  wax,  lingually  and  buccally,  is  left  untouched. 
Into  the  distal  surface  of  the  form,  the  right-angled  exploring  in- 
strument is  stuck  as  deeply  as  possible,  and  an  attempt  made  to 
remove  the  whole  mass  from  the  cavity.  If  this  is  not  successful, 
either  undercuts  are  present,  which  must  be  filled  out  before 
a  further  attempt  is  made,  or  the  wax  is  lodged  against  the 
neck  of  the  adjoining  tooth.  In  the  latter  case  the  wax  in 
the  interproximal  space  must  be  trimmed  with  the  curved 
cement  spatula  (No.  5).  The  mass  removed  from  the  cavity 
is  chilled  in  cold  water,  and  may  then  be  safely  picked  up 
in  the  fingers.  The  cavity  surface  of  the  form  is  examined 
and  any  evidence  of  undercuts  or  projections  which  might 
obstruct  the  removal  of  the  impression,  are  scraped  off  with 
a  small  sharp  spoon  (No.  3).   If  on  the  lower  part  of  the  proxi- 

Bodecker,  Metallic  Inlay.  7 


08 

mal  surface  a  large  surplus  of  wax  is  present,  this  may  be 
removed  partially  before  replacing  the  form  in  the  cavity. 
The  upper  part  of  this  surface,  where  the  wax  lies  against 
the  contact  point  of  the  adjoining  tooth,  should  not  be  dis- 
turbed. 

The  wax  is  then  replaced  in  the  cavity.  If  much  force 
was  necessary  in  removing  the  mass  in  the  first  instance,  the 
wax  should  be  softened  with  warm  water,  and  pressed  snugly 
into  the  cavity  with  the  finger.  On  the  cervical  part  of  the 
proximal  surface  pressure  is  exerted  with  the  spatulate  end 
of  a  Woodson's  amalgam  instrument  (No.  7).  If  the  bite  is 
very  sharp  this  should  be  done  while  the  teeth  are  in  occlusion. 
The  patient  having  occluded,  the  wax,  if  necessary,  is  chilled 
and  the  occlusal  surface  carved. 

A  great  excess  of  wax  on  this  surface  may,  to  save  time, 
be  partially  removed  with  a  warm,  sharp  spatula  (No.  1). 
Usually  it  is  best,  however,  to  do  all  the  scraping  until  the 
margins  of  the  cavity  appear,  with  the  large  spoon  (No.  2). 
Depressions  made  by  the  cusps  of  the  antagonist  are  then 
deepened  with  the  small  spoon.  If  the  bite  is  sharp,  the 
articulation  may  be  controlled,  by  softening  the  surface  of 
the  wax  with  hot  air.  This  must  be  done  with  great  care,  as 
only  the  very  surface  should  be  affected  by  the  heat,  to  avoid 
subsequent  contraction.  Never  should  a  small  body  of  wax, 
or  even  the  neighborhood  of  the  margins  of  a  larger  body, 
be  so  treated.  Upon  cooling,  this  leaves  a  mat  surface  on 
which  the  impressions  of  the  cusps  of  the  antagonist  can 
easily  be  seen.  Such  spots  should  again  be  deepened.  Grooves, 
representing  the  fissures,  are  then  scraped  with  the  instrument 
No.  4.  Only  after  the  occlusal  surface  is  completely  finished, 
should  work  on  the  proximal  surface  be  begun. 

In  order  that  the  wax  form  may  remain  firmly  fixed  as 
long  as  possible,  the  margins  of  the  proximal  cavity  are 
finished  before  modelling  the  proximal  surface.  For  this  pur- 
pose, the  author  prefers  the  three-cornered  probe  (No.  6). 
When  the  edges  are  smooth,  the  probe  is  again  stuck  firmly 
into  the  wax,  preferably  in  the  hole  previously  made,  and 
the  model  lifted  out  of  the  cavity.    An  examination  of  the 


99 

form,  shows  whether  the  margins  have  been  properly  pre- 
pared, and  whether  there  is  still  any  wax  overlapping  the 
margins.  In  this  case  the  form  is  replaced  in  the  cavity,  and 
the  excess  removed.  If  the  point  of  the  probe  should  slip 
over  the  margin  of  the  cavity,  and  remove  to  much  wax, 
more  material  must  be  added  at  this  point. 

The  form  is  placed  in  a  dish  of  cold  water  and  all  adherent 
blood  and  saliva  washed  off  with  a  forcible  stream  of  a  water- 
syringe.  The  form,  held  between  the  fingers,  is  dried  with  the 
cold  blast  of  a  chip  blower.  Wax,  softened  upon  the  spatula 
until  it  just  liquifies,  is  dripped  upon  the  form  as  near  the 
edge  as  possible  at  the  place  to  be  restored.  The  form  is  then 
quickly  replaced  in  the  cavity,  and  the  soft  wax  pressed  over 
the  margin  with  the  spatulate  instrument  No.  7.  This  must 
be  done  before  the  surface  of  the  wax  becomes  moist,  as 
otherwise  the  wax  would  not  unite  where  it  is  accidentally 
folded  in  pressing  the  excess  over  the  margin. 

Modelling  the  contour,  may  be  proceeded  with  when  the 
margins  are  entirely  satisfactory.  For  this  purpose  cloth-strips 
are  of  service.  By  carefully  scraping  the  model,  outside  of  the 
mouth,  just  sufficient  space  to  admit  the  strip  between  the 
form  and  the  adjoining  tooth  is  made.  In  the  neighborhood 
of  the  cervical  margin  the  strip  should  lie  snugly  about  the 
semi-circumference  of  the  tooth,  and  be  gently  drawn  to 
and  fro.  The  nearer  the  contact-point  is  approached,  however, 
the  less  should  the  strip,  at  the  same  time,  encircle  the  whole 
contour  of  the  wax-form.  In  finishing  the  buccal  part  of  the 
proximal  surface,  the  strip  should  enter  the  lingual  side  of 
the  space  loosely,  and  be  drawn  through  in  close  contact  with 
the  buccal  surface  of  the  tooth.  In  finishing  the  lingual  part 
of  this  surface,  the  above  proceeding  is  reserved.  When  the 
wax  is  everywhere  smooth,  and  the  margins  are  perfect,  the 
form  is  definitely  finished.  Before  laying  this  wax  model  aside, 
the  point,  where  the  contact-point  is  to  be  placed,  should  be 
marked.  The  best  way  to  preserve  the  wax  models  is  to  place 
them  in  a  small  dish,  or  glass  containing  cold  water. 

If  regular  undercuts  are  to  be  made  in  the  inlay,  this  may 
be  accomplished  most  easily  upon  the  wax  model,  with  the 


100 

instrument  used  in  scraping  the  fissures  (No.  4).  In  places 
were  the  inlay  is  to  be  specially  roughened,  it  is  advisable 
to  scrape  off  a  thin  layer  of  wax,  in  order  to  increase  the 
space  between  inlay  and  tooth  at  this  point.  If  during  the 
scraping,  the  model  has  been  handled  much,  it  should  be 
given  a  final  trial  in  the  cavity. 

With  slight  modifications,  the  method  of  making  wax 
models  described  above,  may  be  applied  to  all  cavities.  In 
very  large  cavities  it  is  sometimes  of  advantage  to  first  model, 
and  finish  that  part  of  the  form  lying  near  the  margins  of 
the  cavity,  and  later  to  add  sufficient  wax  to  build  up  the 
rest  of  the  form.  Where  but  little  of  the  crown  remains  and 
a  sharp  bite  tends  to  drive  the  wax  out  of  the  cavity,  copper 
rings  will  be  of  service. 

Special  attention  may  be  called  to  the  advantage  offered 
by  the  direct  impression,  in  making  large  contoured  inlays 
under  the  clasps  of  artificial  dentures  already  present  in  the 
mouth.  In  preparing  cavities  of  this  description,  the  pressure 
exerted  upon  the  inlay  by  the  clasp  in  removing  the  denture, 
must  always  be  taken  into  consideration.  The  wax  is  intro- 
duced into  the  cavity,  preferably  with  the  clasp  in  position. 
If  this  is  not  possible,  the  wax  should  be  approximately 
modelled  in  the  cavity  and  the  denture,  with  clasp  well  warmed 
and  oiled,  then  pressed  into  place.  If  the  first  attempt  is  not 
successful  the  procedure  should  be  repeated. 

The  wax  model  to  be  placed  upon  the  sprue  wire,  is  re- 
moved from  the  water  and  laid  upon  a  piece  of  blotting  paper. 
The  sprue  which  should  not  be  of  too  small  a  diameter,  is 
then  heated,  and  a  small  quantity  of  wax  melted  upon  the 
point.  Into  the  wax  model,  held  with  the  proximal  surface 
uppermost,  the  point  of  the  sprue  is  gently  introduced  at  the 
place  marked  as  the  contact  point.  In  mounting  the  form, 
the  sprue  should  never  be  forcibly  pressed  into  the  wax.  As 
soon  as  the  wax  has  set,  the  form  is  replaced  in  cold  water. 
After  casting,  the  added  wax  and  the  sprue-stump  furnish 
sufficient  material  for  the  construction  of  an  ideal  contact 
point  (Fig.  94). 

Beside  a  good  wax  and  proper  instruments,  care  and  prac- 


tice  are  necessary  in  making  a  direct  impression.  The  ad- 
vantages offered,  however,  are  so  numerous,  that  the  writer 
feels  confident,  that  in  time  this  method  will  gain  full  re- 
cognition. Summed  up  briefly  the  advantages  are  the  following: 

1.  The  adaptation  of  the  wax  model  at  the  margins  can, 
with  absolute  certainty,   be   controlled  in  the   mouth. 

2.  By  repeatedly  trying  the  form  in  the  cavity,  and  by 
scraping  away  all  possible  obsctacles,  the  wax  model 
can  finally  be  removed  from  the  cavity  without  dis- 
tortion. 


Fig.  94. 

3.  This  results  in  a  perfect  adaptation  of  the  inlay,  making 
fitting  unnecessary. 

4.  An  ideal  contact  point  can  be  made. 

5.  The  occlusal  surface  is  always  adapted  to  the  case. 

6.  Long   and   tedious   grinding   is   thereby   avoided   while 
setting  the  inlay. 

The  only  disadvantage  which  the  direct  impression  possesses 
is,  that  if  a  failure  in  casting  occurs,  the  time  and  labor  ex- 
pended upon  the  production  of  the  wax  model  is  lost.  Under 
such  circumstances,  the  indirect  impression  method  offers 
the  possibility  of  making  a  second  wax  form  upon  the  model. 
If  the  failures  in  regard  to  adaptation  of  the  inlay  be  exa- 
mined, they  will  be  found  to  depend  upon  three  causes:  1.  an 
inexact  impression,  2.  an  imperfect  model  and  3.  defective 
casting.  If  the  failures  due  to  each  of  these  causes  are 
numerically  compared,  it  will  be  found  that  those  due  to 
defective  casting  are  by  far  less  numerous  than  those  due  to 
each  of  the  other  causes. 


102 

Hollow  wax  models. 

To  partially  obviate  the  greatest  disadvantages  of  the  solid 
metallic  inlays,  that  is,  cost  and  conductivity,  hollow  casting 
has  been  resorted  to.  Castings  of  this  kind  are  made,  either 
by  modelling  the  wax  over  a  core,  or  by  hollowing  out  the 
finished  wax  model.  The  first  method,  as  practised  by  the 
writer,  is  as  follows.  Sodium  bicarbonate  is  made  up  into 
pellets  of  different  sizes,  and  these  when  dry,  are  coated  with 
wax.  For  use,  a  pellet  of  suitable  size  is  warmed,  and  lightly 
pressed  into  the  cavity,  care  being  taken  not  be  approach 
the  margins  of  the  cavity  too  closely  and  to  keep  the  surface 
dry.  Soft  inlay  wax  is  then  introduced  into  the  cavity,  and 
the  form  modelled  in  the  usual  manner.  After  mounting  the 
wax  model  upon  the  sprue,  a  wide  opening  is  made  into  the 


r) 


Fis:.  95. 


bicarbonate  pellet  with  a  hot,  sharp  instrument,  and  the  form, 
then  held  by  the  sprue,  is  dipped  into  dilute  sulphuric  acid. 
The  reaction  is  almost  immediate.  The  opening  into  the 
chamber  must  be  sufficiently  large  to  prevent  the  button  of 
investing  material  from  breaking  off  during  the  process  of 
casting. 

The  second  method,  which  is  perhaps  more  satisfactory 
than  that  described  above,  consist  in  drilling  out  a  chamber, 
or  in  removing  the  necessary  wax  by  aspiration.  For  this 
purpose  F.  E.  Roach  has  constructed  an  instrument  which 
does  good  service.  Roach's  Suction  Wax  Carver  (section. 
Fig.  95)  consists  of  a  small,  thick  walled  metal  bulb,  from 
one  end  of  which  a  smaller  bent  tube  protrudes.  The  other 
end  is  continued  as  a  larger  tube,  covered  with  a  non-con- 
ducting material,  and  serves  as  the  handle  of  the  apparatus. 
The  end  of  this  tube  is  connected  with  the  saliva-pump,  or 
taken  into  the  mouth.    For  use,  a  pledget  of  cotton  is  placed 


103 

in  the  metal  bulb,  and  the  latter  heated  until  smoke  appears 
upon  aspiration.  The  wax  form  mounted  upon  the  sprue  is 
then  hollowed  out.  The  wax  being  melted  by  the  hot  point 
is  sucked  into  the  tube  and  arrested  by  the  cotton  in  the  bulb. 
With  this  apparatus  and  a  suitable  wax,  models  with  extremely 
thin  walls  can  be  produced. 

Though  the  hollow  inlay  does  reduce  the  conductivity  as 
well  as  the  cost  of  production,  it  does  not  give  better  reten- 
tion, as  has  been  so  often  stated.  If  in  hollowing  out  the 
inlay  the  parallel  walls  are  destroyed,  the  retention  is  en- 
dangered, and  the  work  of  having  carefully  prepared  the 
cavity  according  to  certain  mechanical  principles,  will  have 
been  useless.  The  reason,  that  crowns  of  thin  gold  plate 
preserve  a  tooth,  does  not  justify  the  assumption  that  inlays 
of  the  same  thickness  will  be  of  equal  service. 


Chapter  X. 
The  Construction  of  the  Inlay. 

The  methods  according  to  which  metal  inlays  may  be  made, 
can  be  divided  into  two  classes.  In  the  first  class  the  inlay 
is  constructed  upon  a  metal  impression  of  the  cavity,  the 
m.atrix.  In  the  second,  gold  is  cast  in  a  form  exactly  represent- 
ing the  part  to  be  restored.  The  matrix-method  has  been 
entirely  superseded  by  the  casting  process.  The  description 
of  the  methods  of  the  first  class  will  therefore  be  brief,  and 
include  only  the  chief  types. 

Of  these  the  simplest  and  one  of  the  oldest  is  the  method 
suggested  by  ITerbst  (Bremen).  The  impression  was  taken  with 
platinum-gold  foil,  in  the  manner  later  employed  for  porcelain 
inlays.  The  overhanging  edges  were  coated  with  chalk,  and 
the  depression  filled  with  low-fusing  solder  over  an  alcohol- 
flame.  To  facilitate  handling  and  undercutting,  a  piece  of 
gold  wire  was  at  the  same  time  fused  into  the  inlay.  Held 
by  the  wire  in  a  pair  of  pliers,  the  undercuts  were  made  with 
a  saw,  and  the  surplus  of  the  matrix  trimmed  off.  The  wire 
was  then  nipped  off  and  the  inlay  set  and  polished. 

According  to  a  second  method,  whose  originator  is  un- 
known to  the  writer,  the  inlay  is  made  as  follows.  Gold  or 
preferably  platinum-gold  foil  is  adapted  to  the  cavity,  and 
sponge-gold,  under  light  pressure  filled  in,  until  the  contours,etc 
are  restored.  If  the  sponge-gold  does  not  adhere,  the  matrix 
may  be  coated  with  a  sticky  varnish.  The  matrix  is  carefully 
removed  from  the  cavity,  and  the  overhanging  edges  (and  if 
the  bottom  is  torn,  the  lower  surface  also)  coated  with  chalk 
or  rouge.  It  is  then  heated  upon  charcoal,  and  a  strip  of 
18 — 20  kar.  solder  held  upon  the  surface  of  the  sponge-gold 
until  it  becomes  saturated.  Thereupon  the  inlay  is  trimmed 
and  set  in  the  cavity.  A  more  agreeable  color  may  be  pro- 
duced by  using  a  platinum  matrix  and  22  kar.  gold. 


105 

Sponge-gold  inlays  were  also  produced  without  the  use  of 
a  matrix.  According  to  this  method,  still  used  by  some 
practitioners  for  certain  cases,  the  sponge-gold  is  filled  directly 
into  the  cavity,  under  slight  pressure.  At  the  margins  there 
should  be  an  excess  and  a  slight  overlap  of  the  gold.  This  is 
well  burnished  against  the  margin  of  the  cavity.  The  filling 
is  removed  with  a  probe,  the  cavity  surface  coated,  and  then 
saturated  with  16 — 18  kar.  solder.  The  inlay  is  set  and  finished 
in  the  usual  manner. 

In  the  methods  just  described,  the  matrix  was  made  directly 
in  the  cavity ;  in  the  following  methods  a  model  is  necessary  for 
swedging  the  matrix. 

The  inlay  most  extensively  used  before  the  introduction 
of  casting  was,  what  might  for  the  lack  of  a  better  name  be 
called  the  soldered  inlay,  as  it  was  chiefly  composed  of  this 
material.  The  cement  model  of  the  cavity,  made  as  described 
under  the  indirect  impression  method,  is  embedded  in  im- 
pression compound  in  the  cup  of  a  swedging  press.  Platinum 
foil  is  adapted  to  the  model,  and  the  cavity  well  filled  with 
spunk.  The  cup  is  then  placed  in  a  strong  cylinder  with  the 
rubber  cushion  and  plunger  in  position,  and  put  under  strong 
pressure.  The  matrix  is  carefully  removed  from  the  model 
and  the  walls  of  the  cavity  reinforced  with  pure  gold.  It  is 
then  replaced  on  the  model  and  again  put  under  pressure. 
To  prevent  distortion  of  the  matrix,  the  cavity  is  filled  with 
sticky- wax  before  removal  from  the  model.  The  wax  is  burned 
out,  and  the  overhanging  margins  and  the  whole  lower  sur- 
face of  the  matrix  is  coated  with  chalk.  The  cavity  is  then 
filled  out  with  solder,  the  use  of  borax  being  avoided  as  much 
as  possible.  Beginning  with  22  kar.,  and  only  heating  suffi- 
ciently each  time  to  fuse  the  solder  added  last,  the  cavity 
is  gradually  filled  with  22,  20,  18,  and  even  if  necessary  with 
16  kar.  solder.  The  object  should  be  from  the  start  to  place 
sufficient  solder  in  the  cavity  to  complete  the  inlay  in  one 
heating,  without  having  to  add  a  second  or  third  time.  Cusps 
and  contour  are  produced  by  building  up  with  sponge-gold 
and  saturating  with  a  low  grade  solder.  The  inlay  is  finished 
and  set  as  above. 


I 


106 

Larger  parts  of  the  tooth  are  restored,  in  the  following 
manner:  after  the  matrix  has  been  reinforced  and  swedged 
for  the  second  time,  the  missing  contour  is  built  up  in  hard 
wax.  A  piece  of  pure  gold  plate  rolled  extremely  thin,  is 
cut  to  shape,  and  burnished  against  the  wax.  The  plate  should 
lie  in  close  contact  with  the  margins  of  the  matrix.  If  an 
occlusal  surface  is  to  be  restored,  a  suitable  cap  is  swedged 
upon  die-plate  and  waxed  upon  the  matrix.  A  part  of  one 
surface,  proximal  or  occlusal,  must  always  remain  uncovered 
for  the  introduction  of  the  solder.  With  the  exception  of  this 
opening,  the  matrix  with  the  wax  and  plate  is  embedded  in 
asbestos  powder.  After  drying,  the  wax  is  burned  out  and 
the  chamber  filled  with  solder. 

The  inlays  described  so  far  are  all  solid,  a  large  number 
of  methods,  however,  have  been  suggested  for  making  hollow 
swedged  inlays.  The  following  method,  devised  in  its  essen- 
tials by  Hinman  (Atlanta),  is  as  follows.  For  swedging,  the 
small  S.  S.  White  press  was  used.  The  impression  of  the 
cavity,  taken  in  the  usual  manner,  is  embedded  in  moldine, 
and  well  oiled.  The  cup  of  this  press  is  inverted  over  the 
impression  and  through  the  hole  in  the  bottom  of  the  cup 
"inlay- metal",  an  improved  Spence  metal,  is  poured.  The 
model  being  cleaned,  is  ready  for  immediate  use. 

The  matrix  should  be  made  of  rolled  gold  No.  60.  Platinum 
gold  of  this  thickness  is,  however,  preferable.  The  foil  is  adapted 
to  the  model  and  covered  with  a  rubber  disk.  The  cylinder 
of  the  press  is  filled  with  moldine,  placed  over  the  cup  and 
the  plunger  introduced.  The  latter  is  given  a  few  light  blows 
with  a  heavy  hammer.  The  matrix  is  removed,  reinforced, 
a  hole  cut  into  the  bottom,  and  then  reswedged.  The  model 
is  then  filled  with  wax,  and  the  contour  and  occlusal  surface 
carved.  If  possible  this  wax  model  is  tried  in  the  mouth. 
The  wax  is  again  placed  upon  the  Spence  model,  the  surfaces 
smoothed,  and  an  amount  carved  away  from  the  margins  of 
the  cavity  equal  to  the  thickness  of  the  gold  used  for  outer 
part  of  the  inlay.  An  impression  of  the  wax  form  is  then 
taken  and  cast  in  "inlay  metal".  The  cap  swedged  upon  this 
second  model,   is   carefully  soldered  from  the   outside  with 


107 

20  kar.  solder  upon  the  matrix,  while  through  to  hole  cut  in. 
the  bottom,  the  inside  is  thoroughly  reinforced  with  14 — 16kar. 
solder.  In  setting  the  inlay  into  the  cavity,  the  chamber  is 
filled  with  cement. 

For  making  this  class  of  inlays  (Fig.  57),  preeminent  before 
the  introduction  of  casting,  a  large  number  of  methods  have 
been  devised.  To-day  such  inlays  are  never  made.  Their  dis- 
advantage is  not  alone  the  difficulty  of  construction,  but  also 
the  inadaptability  of  the  margin,  as  a  result  of  soldering 
the  two  parts  together.  The  hardness  of  the  gold  makes 
burnishing  the  margins  impossible.  The  only  advantages 
which  at  that  time  could  be  claimed  for  this  class  of  inlays 
were,  that  they  saved  valuable  metal,  and  that  being  filled 
with  cement,  they  were  not  as  good  conductors  of  temperature 
as  solid  metallic  fillings. 

The  Casting  Process. 

The  wax  model,  mounted  as  described  on  page  100,  is  washed 
off  with  alcohol.  The  sprue  is  placed  upon  the  sprue-holder,  and 
together  with  the  model,  coated  with  investment  material  of 
creamy  consistency.  The  cup  or  casting-ring  is  then  filled  with 
the  same  material,  the  sprue-holder  inverted,  and  allowed  to 
gently  settle  down  until  its  edges  are  in  contact  with  the 
cup;  or  the  ring  may  be  placed  in  position  and  filled  from 
above.  The  investment  material  must  be  so  soft,  that  pressure 
is  never  necessary  in  embedding.  As  soon  as  the  investment 
has  set,  the  sprue-holder  is  removed,  and  the  form  gently 
heated  until  the  sprue  can  be  withdrawn.  The  heat  is  then 
gradually  increased.  In  about  half  an  hour  the  wax  has  been 
thoroughly  burned  out,  and  a  smooth  walled  chamber  remains. 
The  form  is  then  ready  to  be  cast  by  any  one  of  the  different 
casting  processes. 

The  investment  material. 

Before  describing  the  different  systems  of  casting  inlays, 
a  few  words  on  the  subject  of  investment  materials,  and  on 
the  casting  of  metals  in  general  are  deemed  necessary.    All 


108 

of  the  innumerable  materials  recommended  for  the  investment 
of  metallic  inlays  are  by  no  means  satisfactory  in  practice. 
Which  of  these  is  the  best,  or  if  any  one  of  them  possesses 
all  the  necessary  qualities  of  a  perfect  investment  material, 
are  questions  that  can  be  determined  only  by  a  long  series 
of  experiments  or  comparative  tests. 

The  qualities  which  an  ideal  material,  used  as  an  invest- 
ment for  the  production  of  inlay  casting-forms  should  possess, 
are  briefly  summed  up  below. 

1.  The  material  mixed  to  a  thick  creamy  consistency,  should 
set,  without  contracting,  within  a  quarter  of  an  hour. 

2.  In  drying  and  heating  the  mold,  the  material  should 
neither  crack,  burn,  fuse,  soften  or  change  its  form  in 
any  way. 

3.  After  the  wax  has  been  burnt  out,  the  walls  of  the 
form  should  be  perfectly  smooth. 

4.  The  material  should  be  sufficiently  porous,  to  permit 
the  escape  of  the  air  compressed  in  the  form  during 
casting. 

5.  A  quality  which  the  material  should  possess  in  a  high 
degree,  is  non-conductivity  of  heat.  The  more  marked 
this  quality  in  an  investment,  the  less  need  the  metal 
to  be  cast,  be  heated  above  its  fusing  point. 

6.  The  material  must  be  hard  enough,  and  possess  suffi- 
cient edge-strength,  to  withstand  the  pressure  of  casting. 

7.  The  material  should  not  be  disintegrated  by  the  heat 
of  the  molten  metal.  An  investment,  unsatisfactory  as 
regards  the  last  two  points  (6  and  7),  cannot  be  used 
to  cast  inlays  of  complex  form.  The  angles,  which  on 
the  cavity  surface  of  the  wax  model  were  well  defined, 
would  in  the  inlay  appear  quite  rounded.  The  inlay 
would  then  not  fit  into  the  cavity. 

8.  The  investing  material  should  contain  no  substance, 
which  under  the  action  of  the  heat  of  the  molten  metal, 
becomes  adherent  to  the  surface  of  the  inlay. 

To  prevent  the  formation  of  bubbles,  the  material  must 
be  slowly  and  carefully  mixed.  Though  some  investments  are 
more  liable  than  others  to  the  formation  of  bubbles,  correct 


lOIJ 

mixing  and  embedding  will  usually  obviate  this  difficulty. 
Tapping  the  cup  or  ring  after  the  wax  model  has  been  em- 
bedded will  inevitably  lead  to  the  formation  of  bubbles.  The 
cup  is  tapped  on  the  supposition  that  all  bubbles  will  thereby 
rise  to  the  surface.  This  is,  however,  not  the  case.  Gas  bubbles 
are  strongly  attracted  by  any  foreign  body  present  in  a  liquid 
or  semi-liquid  medium.  The  bubbles  will  therefore  collect 
upon  the  surface  of  the  wax-model,  and  no  amount  of  tapping 
can  then  dislodge  them. 

A  number  of  methods  have  been  suggested  for  the  pre- 
vention of  bubbles  in  the  investment.  The  simplest  is  pro- 
bably the  use  of  recently  boiled  water.  The  writer  found  this 
to  be  used  in  the  arts,  in  making  fine  plaster  casts*).  Contrary 
to  expectations,  this  procedure  has  given  very  satisfactory 
results.  Another  method,  suggested  by  the  writer,  is  to  place 
the  water  or  even  the  ready  mixed  investment  material  under 
the  bell -jar  of  an  exhaust  pump.  After  exhauting  the  air, 
the  wax-model  is  carefully  embedded  in  the  usual  manner. 
The  necessity  of  an  expensive  apparatus,  is  the  objection  to 
this  method.  Price**),  on  the  other  hand,  compresses  the  air 
contained  in  the  investment  material.  The  top  of  the  cup, 
with  the  recently  embedded  model  is  covered  with  a  layer  of 
wax  and  placed,  until  the  investment  has  set,  in  a  hydraulic 
press  capable  of  exerting  a  pressure  of  70 — 80  atmospheres. 
The  plastic  material  is  thereby  forced  into  the  finest  details 
of  the  wax  form,  and  the  bubbles,  in  obedience  to  the  law 
of  the  volume  of  gases  under  pressure,  are  decreased  to  ^/^o 
or  i/so  of  their  normal  volume.  Price  says:  "This  produces 
a  model  of  great  density  and  smoothness  of  surfaces,  and 
when  applied  to  an  investment  around  a  wax-model  has  a 
most  beautiful  effect  on  the  surface  of  the  cast  gold,  and  the 
greatly  increased  density  produces  a  harder  investment,  and 
one  with  greater  expansion."  The  latter  is,  according  to  Price, 
a  very  valuable  quality.  He  argues,  that  as  cast  gold  even 
under  the  most  favorable  circumstances  shows  a  contraction 


*)   Ed.  Uhlenhuth,   Formen  und  GieBen  (Leipzig). 
**)  Weston  A.  Price,  The  Laws  Determining  Casting  or  Fusing  Results,  etc. 
Items  of  Interest  No.  3,  5  u.  6,  1908.    ' 


110 

of  1.3  per  cent,  an  investment  material  with  an  expansion  of 
exactly  the  same  amount,  would  correct  this  error.  Such  an 
ideal  investment  material,  having  all  the  other  necessary  quali- 
ties, has  as  yet,  not  been  produced. 

The  amount  of  material  used  for  investing,  and  consequently 
the  size  of  the  cup,  should  be  in  proportion  to  the  size  of  the 
wax-model.  As  all  investments  expand  more  or  less  upon 
being  heated,  the  walls  of  the  mould  should  be  of  the  same 
thickness  at  all  points.  This  insures  a  uniform  expansion, 
preserving  the  correct  proportion  in  the  inlay.  If  a  wall  is 
thin,  yet  sufficiently  strong  to  withstand  the  pressure  of  casting, 
it  will  expand  less,  and  consequently  the  inlay  will  be  flattened 
on  that  side.  If  the  wall  cannot  withstand  the  pressure, 
it  will  either  be  bulged  out  or  cracked  in  casting.  "The  best 
that  any  of  the  investments  now  available  will  do  is  to  expand 
8,5  thousanths*)  as  a  maximum  at  1000  degrees  F."  (Price), 
and  as  the  metal  of  a  steel  or  brass  cup  has  a  coefficient  of 
expansion  of  about  twice  this  amount,  it  becomes  evident, 
that  the  mould  receives  but  little  support  from  the  cup  or 
ring  when  it  is  heated.  This  proves  the  necessity  of  making 
the  walls  of  the  mold  sufficiently  thick. 

Price  calls  attention  to  the  fact  that  the  investment  must 
be  homogeneous.  His  experiments  have  proven,  that  different 
investment  materials  do  not  expand  equally,  and  that  this 
is  true  of  even  a  thin  and  a  thick  mix  of  the  same  material. 
If  therefore  the  wax  model  is  coated  with  a  thin  mix,  and  the 
cup  filled  with  a  thicker  mix  of  the  same  material  or  even 
with  another  investment,  failure  becomes  imminent,  owing  to 
unequal  expansion  of  the  mould.  Cracks  and  crevisses  are 
formed,  or  the  inner  layer  of  investment  may  in  places  break 
away  from  the  outer. 

The  mould  should  be  dried  slowly  and  uniformly.  If  the 
investment  contains  much  plaster,  drying  may  be  more  rapid. 
The  water  and  wax  boil  out  of  the  sprue  gate  without  doing 
the  mould  any  harm.  The  disadvantage  of  such  material  is 
that  it  checks  easily  in  heating,  and  that  it  is  disintegrated 


*)  Taggart's  Investing  Material. 


Hi 

by  tlie  heat  of  the  metal.  After  the  mould  is  dry,  it  must 
be  further  heated  to  burn  out  every  trace  of  wax.  Tests  made 
by  the  writer  have  shown  that  this  takes  place  at  a  tempera- 
ture of  about  450  °C.  (842  degrees  F.)  The  wax  passes  off 
as  a  blue  vapor,  and  a  deposit  of  carbon  blackens  the  sprue- 
gate.  Continued  heating  causes  the  deposit  to  disappear 
gradually  until  the  gate  has  resumed  its  natural  color,  only 
a  dark  ring  remaining  upon  the  surface  of  the  mould.  Every 
trace  of  wax  has  then  been  burned  out,  and  the  temperature 
in  the   chamber  of  the  mould  is  about  850 — 900  degrees  F. 

With  some  investments,  it  is  not  advisable  to  allow  too 
long  a  time  to  intervene  between  embedding  the  model  and 
burning  out  the  wax.  While  standing  the  investment  looses 
moisture,  so  that  when  the  mould  is  heated,  the  wax  instead 
of  boiling  out  of  the  sprue-gate  with  the  water,  is  absorbed 
by  the  investment.  This,  in  some  cases,  seems  to  have  a  dele- 
terious effect,  producing  an  inlay  with  very  rough  surfaces. 
The  same  effect  is  produced  by  heating  such  investments 
too  slowly. 

An  investment  material,  perfect  in  every  respect,  is  up 
to  date,  unknown  to  the  writer.  Price's  artifical  stone,  though 
not  an  investment  in  the  strictest  sense,  possess  many  of  the 
most  desirable  qualities.  It  is  a  body  equally  related  to  the 
Portland  and  silicate  cements.  For  mixing  an  orthophosphoric 
acid  of  definite  specific  gravity  is  used.  This  material  is  hard, 
dense,  and  very  resistent  to  temperatures  up  to  2700  degrees  F. 
Its  linear  coefficient  of  contraction  in  setting  is  "in  some  cases 
as  low  as  two-thousandths  per  linear  inch".  The  stone  model 
is  made  from  an  impression,  the  cavity  in  the  model  waxed 
up,  and  the  model  with  the  wax  in  position  embedded  in 
investing  material  in  the  usual  manner. 

An  investment  recommended  by  W.  Sachs  (Berlin),  and 
extensively  used  in  the  northern  part  of  Germany,  consists  of 

Quartz  flour      2  parts 

Plaster 1  part  (by  volume). 

The  quartz  flour,  an  almost  perfectly  pure  silica,  is  ob- 
tained from  the  Koyal  Prussian  Porcelain  Factory.  The  in- 
gredients should  be  well  mixed,  preferably  in  a  rotary  flour 


112 

sieve.  Another  investment,  which  has  been  recommended  by 
Arvine*),  consists  of 

Enghsh  porcelain  clay     .      1     part 

Quartz  flour 1     part 

Plaster 1,5  parts  (by  weight). 

M.  L.  Ward  (Ann  Arbor)*)  after  carefully  studying  the 
subject  of  investing  materials,  believes  that  a  material  for 
this  purpose,  to  be  strong,  must  have  a  composition  ana- 
logous to  that  of  concrete.  This  is  a  mass  composed  of  gravel 
in  which  the  spaces  are  filled  out  by  sand,  and  the  spaces 
beween  the  grains  of  sand  are  in  turn  filled  out  by  cement. 
In  the  investment  suggested,  the  gravel  is  represented  by  flint 
powder,  the  sand  by  quartz  flour,  and  the  cement  by  plaster. 
The  proportions  as  given, 

Fhnt      30  cc. 

Quartz  flour 36  cc. 

Plaster  of  Paris 17  cc. 

refer  only  to  the  materials  used  by  Dr.  Ward.  The  grit  of 
the  silicates  and  the  quality  of  the  plaster  are  the  factors 
which  determine  the  relative  quantities  of  the  formula. 

The  casting-metal. 

Only  the  noble  metals  and  their  alloys  are  used  in  casting 
inlays.  They  possess  all  the  qualities,  necessary  for  sucessful 
casting.  These  metals  may  be  fused  with  the  flame  of  an 
ordinary  blow-pipe,  and  become  sufficiently  fluid  to  reproduce 
the  finest  details  of  the  mold.  In  common  with  all  metals, 
they  possess  the  property  of  contracting  after  having  been 
cast.  The  contraction  occurs  in  three  different  stages;  1.  con- 
traction of  the  overheated  metal  in  its  liquid  state,  2.  con- 
traction at  the  moment  of  solidification,  and  3.  contraction 
of  the  solid  metal  while  cooling.  An  exception  to  this  rule 
is  made  by  cast-iron,  bismuth,  and  some  alloys  of  copper 
and  tin.  These  expand  more  or  less  at  the  moment  of  solidifi- 
cation.   In  the  third  stage  they  again  act  like  other  metals. 

*)  F.  B.  Arvine,  Gold  Cast  Inlay  Investment,  Cosmos,  No.  1,  1908. 
**)  Marcus  L.  Ward.'    A  Consideration  of  the  Casting  Process,  with  Special 
Reference  to  Refractory  Materials.      Dental  Cosiaos,  Sept.   1909. 


113 

'     Uhlenhuth  gives  the  linear  coefficient  of  contraction  of 
some  of  the  baser  metals  as: 

from  to       average 

Zink V65  V57         V62 

-L'SaCl /l04  /sG  /92 

liri /173  /i2(,  /147 

Statuary-bronze    ....       —  —         ^/i2o 

-t>rass /79  749  /eg 

Cast  iron Ves  V95         Vse 

Gun-metal      V139         V130        V135 

(100  copper,   12 V2  tin) 

Bell  metal —  —         ^/es 

(100  copper,  18  tin) 

Steel —  —         i/e.5 

"The  cubical  coefficient  of  contraction,  is  found  by  trebling 
the  above  fractions  while  for  the  coefficient  for  a  surface,  the 
fractions  are  doubled.  A  cube  of  cast-iron  will  therefore  shrink 
along  each  edge  ^/gg,  upon  each  surface  '^1^^  and  in  cubical 
contents  ^/32." 

In  regard  to  the  shrinkage  of  the  noble  metals  as  determined 
by  W.  A.  Price,  the  appended  table,  though  incomplete,  shows 
some  interesting  points.  The  linear  coefficient  of  contraction 
is  given  in  thousandths.  The  influence  of  pressure  upon 
shrinkage  is  also  shown. 


Pressure 

Gold 
24  kar. 

Gold 
18  kar. 

Gold  solder 

Gold  18   \ 
Silver  2    1 
Copper  2  {^^^^^ 

Silver  (pure) 

Gold  and 

10% 
Platinum 

Zink  2     ] 

0 

22.5(V45)*) 

— ■ 



. 



V50  oz. 

20.5 



18 





/lO       55 

18 



— 





3   pounds 

14 



— 

20  (V50) 



5V2    55 

13  (V77) 

15.5 

15 

— 

14 

*)   Converted  into  fractions  as  in  the  table  of   Uhlenhuth. 


That  the  gold  used  in  casting  an  inlay  does  shrink,  is  an 
indisputable  fact.    The  amount  of  shrinkage,  as  well  as  the 


Bodecker,  Metallic  Inlay. 


114 

best  metliod  of  controlling  it,  are  subjects  upon  which  opin- 
ions differ  widely.  Ward*)  beleives  the  shrinkage  in  a  pro- 
perly cast  inlay  to  be  far  below  the  percentage  given  by 
Price.  As  the  coefficient  of  contraction  of  cast-iron  decreases 
in  direct  proportion  with  the  size  of  the  casting,  Dr.  Lane 
argues  by  analogy,  that  as  Price  determined  the  percentage 
of  shrinkage  on  gold  bars,  the  percentage  of  a  small  inlay 
would  be  proportionately  less.  Upon  this  theory,  the  actual 
shrinkage  of  a  pure  gold  inlay  of  V4  inch  in  diameter  is  stated 
to  be  0,0008  in.  This  leaves  a  space  of  0,0004  in.  on  each 
side  between  the  walls  of  the  cavity  and  the  inlay.  This 
could  be  filled  only  with  the  finest  grained  cement.  (See  Head's 
table  p.  140.)  The  progressive  variation  in  the  coefficient  of 
contraction  is  accounted  for  by  the  more  rapid  chilling  of 
the  smaller  masses  of  metal  immediately  after  being  cast. 
In  order  to  cast  inlays  with  such  low  shrinkage,  the  mold 
should  be  cool,  and  the  gold  as  fluid  as  possible  without  being 
heated  much  above  its  fusing  point.  The  casting  machine 
must,  therefore,  be  quick  and  reliable  in  action. 

Lane**)  found  by  a  series  of  experiments,  that  the  amount 
of  pressure  has  no  influence  on  shrinkage,  as  long  as  an  ex- 
ceedingly hot  mold  is  used.  Equally  good  results  were 
obtained  by  using  45  or  5  pounds  pressure  per  square  inch. 
Castings  made  from  a  half-inch  pattern,  showed  a  shrinkage 
of  0,0008  inch. 

Van  Horn***)  recommends  the  use  of  a  superheated  mold. 
He,  however,  does  not  believe  that  this  measure  alone  will 
prevent  shrinkage.  This  is  accomplished  by  determining  the 
coefficient  of  expansion  of  the  wax  used,  and  making  the 
mold  with  a  correspondingly  hot  investing  material.  (115  to 
120°  F.)  The  wax  expanding  uniformly,  produces  a  slightly 
enlarged  mold,  which  in  turn  neutralizes  the  contraction  of 
the  gold.  By  this  method,  it  is  possible  to  produce  castings 
which  are  even  larger  than  the  patterns. 

*)  M.  L.  Ward.  A  Consideration  of  the  Casting  Process  etc.  Dental  Cosmos, 
Sept.  1909. 

**)  Dental  Digest,  July,  1909,  p.  498. 
***)  C.  S.  van  Horn.     Casting:    A  Review  and  Commentary,   etc.      Dental 
Cosmos,  August  1910. 


115 

Price*),  in  regard  to  shrinkage,  says  "that  gold  does  con- 
tract a  definite  amount  no  matter  when,  how,  or  by  whom 
it  is  manipulated,  and  that  this  total  contraction  will  take 
place  under  all  conditions,  though  its  exact  position  may  be 
changed  in  part;  that  is,  as  the  mass  of  gold  making  up  the 
inlay  and  sprue  is  cooling,  the  gold  may  be  moved  from  the 
sprue  to  take  up  some  of  the  total  of  the  contracted  gold 
in  the  inlay."  In  another  article  Price  claims  that  "the 
location  of  the  shrinkage  or  contraction  (not  the  total  amount) 
can  be  partially  transferred  to  another  part  of  the  cooling 
mass  by  pressure  on  the  molten  gold  while  it  is  in  a  semi- 
molten  state,  and  that  the  distance  or  range  in  temperature 
below  the  melting  or  fluid  point  through  which  it  can  be 
moved  from  one  part  of  the  mass  to  another  to  take  the 
place  of  contraction  at  that  latter  place,  is  dependent  upon 
the  pressure  used."  Price  therefore  claims  that  high  pressure 
is  the  only  reliable  means  of  preventing,  or  at  least  con- 
trolling, shrinkage.  This,  of  course,  necessitates  the  use  of 
high  pressure  machines  in  connection  with  the  stone  model, 
as  ordinary  investments  v/ould  under  such  circumstances  be 
worth  less. 

From  the  opinions  quoted,  it  becomes  evident  that  this 
question  is  far  from  being  settled.  Granting  the  accuracy  of 
the  experimental  data  in  each  case,  it  remains  for  future  in- 
vestigations to  prove  the  fallacy  of  some  of  the  deductions. 

Mention  has  been  made  of  the  fact,  that  the  shrinkage  of 
metals  occurs  in  three  stages. 

1.  Shrinkage  of  the  molten  metal. 

2.  Shrinkage  daring  solidification. 

3.  Shrinkage  of  the  solid  metal  upon  cooling. 

For  gold,  only  the  shrinkage  during  the  third  stage  has  been 
investigated.  It  may  be  safely  assumed  that  any  measure 
taken  to  influence  the  shrinkage  in  this  stage  will  have  but 
very  little  effect.  Price  found  that  the  melting  point,  and 
therefore  also  the  point  of  solidification,  of  gold,  could,  by  high 

*)  Weston  A.  Price.  Some  Adv^antages  of  the  Stone  Model  Method  etc. 
Dental  Cosmos,  Sept.  1910. 

**)  Items  of  Interest,  Sept.   1910. 

8* 


116. 

pressure,  be  reduced  as  much  as  200°  F.  The  question  arises 
whether  the  pressure  prolongs  the  process  of  crystaUization, 
or  whether  the  point  is  simply  reduced  200°,  while  the  pro- 
cess itself  goes  on  in  the  time  and  manner  as  under  normal 
conditions.  Price  believes  that  as  gold  shrinks  0,001  with 
every  100°  F.  under  the  fusing  point,  by  lowering  the  fusing 
point  200°,  the  shrinkage  is  reduced  by  0,002.  A  thorough 
investigation  of  the  phenomena  in  the  second  stage  of  shrink- 
age (solidification)  will  probably  explain  why  contrary  methods 
of  casting  seem  to  give  the  same  results.  That  metals  in  this 
stage  obey  some  special  laws,  is  proven  by  the  fact  that  cast- 
iron,  in  contradistinction  to  most  other  metals,  expands  to 
such  an  extent  during  solidification,  that  it  is  liable  to  burst 
all  but  the  strongest  molds. 

Any  metal  heated  above  its  fusing  point,  will,  with  in- 
creasing temperature,  constantly  expand.  After  casting  an 
inlay,  the  pressure  equalizes  the  resultant  contraction  up  to 
the  moment  of  solidification,  by  forcing  liquid  metal  into  the 
mould  to  counteract  the  shrinkage.  If,  however,  the  channel 
is  long  and  narrow,  the  material  used  for  investment  not 
a  poor  conductor,  and  the  metal  overheated,  then  the  metal 
in  the  channel  will  solidify  while  the  metal  in  the  cavity 
of  the  mould  is  still  liquid.  When  the  latter  gradually  cools, 
no  additional  metal  can  then  be  forced  into  the  mould  to 
replace  the  shrinkage.  The  dead-head,  or  excess  metal  in  the 
channel,  usually  parts  from  the  casting  at  the  point  where 
it  enters  the  chamber  of  the  mould.  This  condition,  known 
as  blowing,  is  recognized  on  an  inlay  by  the  presence  of  more 
or  less  irregular  depressions  about  the  dead-head.  The  latter 
does  not  always  tear  away  from  the  inlay  and  may  be  normal 
in  appearance,  in  spite  of  the  presence  of  blow-holes.  Foreign 
matter  in  the  casting  metal  may  produce  the  same  conditions, 
by  obstructing  the  free  flow  in  the  channel.  To  prevent  the 
formation  of  blow-holes,  special  attention  should  be  paid  to 
the  quality  of  the  investment  used,  as  well  as  to  the  cleanness 
and  the  heating  of  the  metal.  The  reason  for  using  a  short 
sprue,  which  in  diameter  is  proportionate  to  the  size  of  the 
inlay,  is  evident.    Perfect  fluidity  of  the  metal  is  absolutely 


117 

essential  to  successful  casting.  Foreign  matter,  traces  of  in- 
vesting material,  products  of  oxidation,  and  other  metals  are 
contaminations  which  tend  to  reduce  the  fluidity  of  the  metal, 
and  should,  therefore,  be  carefully  removed  before  casting. 
Foreign  matter  need  be  considered  only  if  the  gold  has  been 
accidentally  spilled.  Investing  material  can  be  removed  by 
dilute  hydrofluoric  acid.  The  products  of  oxidation  and  other 
metallic  contaminations  are  removed  only  by  refining  the  gold. 
For  this  purpose  Ward*)  recommends  the  dry  process.  "A 
number  of  different  methods  of  purifying  gold  might  be 
enumerated,  but  perhaps  nothing  will  ever  be  of  more  service 
than  about  equal  parts  of  potassium  nitrate  and  borax.  Both 
are  clean  white  powders  which  can  be  mixed  and  kept  in  an 
accessible  place.  If  a  casting  is  about  to  be  made,  and  the 
gold  is  found  to  be  too  sluggish,  the  operation  need  not  be 
delayed  much  over  five  minutes  to  purify  the  gold,  while 
ten  or  fifteen  minutes  v/ould  raise  the  karat  considerably.  The 
process  involves  the  oxidation  of  the  base  metals,  the  oxygen 
being  furnished  by  the  potassium  nitrate,  and  these  oxids  being 
separated  from  the  gold  beneath  the  flux  of  borax.  The  gold 
should  be  melted  and  the  mixture  added  a  little  at  a  time 
with  one  hand,  and  a  blowpipe  flame  kept  directed  on  the 
gold  v/ith  the  other,  the  gold  all  the  time  being  kept  melted. 
This  should  be  continued  in  most  cases  for  about  five  minutes, 
though  it  is  often  necessary  to  continue  the  process  much  longer. 
As  soon  as  the  last  particles  of  nitrate  and  borax  have  been 
put  on  the  gold  the  flame  should  be  removed,  to  avoid  its 
contaminating  influence.  Gold  known  to  contain  certain  quan- 
tities of  tin,  silver,  or  lead  could  perhaps  best  be  refined  by 
the  ammonium  or  mercuric  chlorid  process,  but  for  iron,  bis- 
muth, antimony,  zinc,  etc.,  nothing  excels  potassium  nitrate 
and  borax." 

The  metal  almost  exclusively  used  in  casting  inlays,  is  gold. 
Opinions  differ,  however,  in  regard  to  the  fineness.  Most 
operators  prefer  to  use  22  kar.  gold,  while  the  writer,  for 
reasons  described  in  chapter  II  and  XI,  generally  makes  his 
inlays  of  24  kar.    In  cases  where  the  anchorage  extension  must 

*)  M.  L.  Ward,  Dental  Cosmos.     Sept.  1909. 


118 

bear  considerable  strain,  or  where  abraded  occlusal  sur- 
faces are  to  be  restored,  22  kar.  gold  is  undoubtedly  pre- 
ferable. 

A  number  of  inlays  of  pure  silver  have  been  made  by  the 
writer.  The  only  objection  to  this  metal  is  that  it  often 
turns  black  in  the  mouth.  It  casts  well,  and  can  without 
difficulty  be  burnished  against  the  margins  of  the  cavity. 
Being  as  servicable  as  gold  and  requiring  the  same  cavity 
preparation,  yet  costing  much  less,  the  silver  inlay  would  be 
of  use  in  college  infirmary  practice. 

Though  platinum  can  be  cast  in  special  apparatus,  its  high 
melting  point  makes  its  use  in  inlay  work  almost  impossible. 
The  writer  has  cast  inlays  of  this  metal,  using  the  Jameson 
apparatus  and  a  gas -oxygen  flame,  and  melting  the  metal  in 
a  specialy  constructed  crucible.  The  results  were  only  occa- 
sionally satisfactory.  Platinum  inlays  would  be  useful,  for  com- 
bination with  high-fusing  porcelain  (Figs.  102 — 105).  Dental 
alloy,  silver  and  platinum,  does  not  always  keep  its  color  in 
the  mouth. 

Gold,  owing  to  its  color  and  its  contraction,  cannot  be 
designated  as  an  ideal  material  for  making  inlays.  Such  a 
metal  would  have  to  be  constant  in  form,  and  possess  the 
durability  and  malleability  of  gold,  the  cheapness  of  silver  and 
soft  lustrous  color  of  aluminum. 


The  casting  apparatus. 

A  description,  or  even  an  enumeration  of  all  the  apparatus, 
which  have  been  suggested  or  put  on  the  market  would  almost 
be  impossible,  as  their  number  at  present  exceeds  one  hundred. 
Neither  can  special  directions  for  use  be  given  in  describing 
the  principles  of  each  class  of  apparatus,  as  the  author's  ex- 
perience is  limited  to  but  a  few,  and  all  directions  necessary 
may  be  obtained  from  the  manufacturer. 

According  to  the  manner  in  which  the  pressure  is  pro- 
duced, all  machines  used  for  casting  inlays  may  be  divided 
into  five  classes.  The  pressure  is  produced  in  the  different 
classes  by,  — 


119 


1.  (jas, 

2.  Steam, 

3.  Direct  contact, 

4.  Centrifugal  force, 

5.  Vacuum. 

An  example  of  each  class  will  be  described,  and  the  action 
of  the  pressure  upon  the  molten  metal  and  upon  the  mould, 
briefly  explained. 

1.    Gas  Pressure  (Pneumatic  force). 

This  class  includes  all  machines  using  compressed  gases, 
as  nitrous  oxid,  carbon  dioxid,  or  air.  The  eldest  of  this  class, 
and  at  the  same  time  the  first  machine  for  the  purpose  of 
casting  inlays,   was  invented  by  Taggert   (Fig.  96).    In  this 


Fi</.  9G. 


120 

apparatus  the  compressed  gas,  nitrous  oxid  is  not  only  used 
for  the  production  of  pressure  in  casting,  but  also  as  a  flame 
to  melt  the  metal.  From  the  cylinder  the  gas  flows  through 
the  reduction-valve  {a)  to  the  stop-cock  (h),  then  through  a 
rubber  tube  to  the  burner  (c).  The  flame  strikes  the  sprue- 
gate  of  the  mold  {d),  where  the  metal  to  be  fused  is  placed. 
By  regulating  the  reduction-valve  and  observing  the  gage, 
the  pressure  deemed  necessary  in  each  case,  is  set  before 
casting.  When  the  gold  is  sufficiently  heated,  the  lever  (/) 
is  quickly  pressed  down.  The  cam  {i)  pressing  against  the 
arm  (o),  turns  the  burner  aside  and  extinguishes  the  flame, 
at  the  same  time  permitting  the  gas  to  pass  from  the  valve  {a), 
at  the  pressure  perviously  determined,  through  the  tube  (e) 
to  the  head  (A).  Five  small  holes  in  the  middle  of  the  under 
surface  of  the  head  serve  to  admit  the  gas  to  the  mold,  while 
a  packing  pressing  on  the  edge  of  the  casting-ring  prevents 
escape. 

In  all  machines  of  this  class,  the  action  taking  place  in 
the  mold  is  the  same.  The  gas  in  pressing  upon  the  surface 
of  the  molten  metal  drives  it  into  the  mould.  The  gold  in  turn 
compresses  the  air  contained  in  the  cavity  of  the  mold,  thereby 
forcing  the  latter  into  the  porous  investment. 

In  regard  to  the  effective  pressure  in  the  mold,  Price  says: 
"When  the  pressure  is  obtained  from  gas  or  air  it  is  equal 
to  the  cross  section  area  of  the  inlay  or  mold,  not  the  gate 
or  sprue,  in  fractions  of  a  square  inch  divided  into  the  pressure 
per  square  inch  of  the  gas.  For  example,  if  the  cross  section 
area  of  the  inlay  is  ^/g  of  an  inch  square,  it  will  be  ^/^^  of  a 
square  inch,  and  the  pressure  16  pounds  per  square  inch,  the 
effective  pressure  will  be  ^/^^  of  16,  or  ^/^  of  a  pound,  less  the 
back  pressure  of  the  gas  retained  in  the  investment  behind 
the  gold,  and  the  leakage  of  the  pressure  around  the  gold, 
for  if  the  pressure  can  get  away  through  the  investing  material 
easily  from  behind  the  gold,  it  can  easily  get  past  around  it 
in  the  same  way;  which  means  that  there  would  be  con- 
siderably less  pressure  than  ^/^  pound,  depending  largely  on 
the  compactness  of  the  investing  material  and  the  leakage 
of  the  closing  device  over  the  molten  gold.   The  writer  believes 


121 

the  effective  pressure  under  the  above  conditions  to  be  less 

than  ^/s  of  a  pound  actual  pressure." 

It  becomes  evident  from,  the  above  observations,  that  the 

action  of  the  pressure  in  machines  of  this  class  must  be  rapid 

and  intense,  to  prevent  the  penetration  of  the  gas  into  the 

investment.    Another  fact  to  be  borne  in  mind  is,  that  the 

pressure  indicated  by  the  gage  does  not  correspond  to  the 

pressure  in  the  mold,  as  there  is  always  more  or  less  leakage 

through  the  packing  between  the  head  and  the  ring  of  the 

mold. 

2.    Steam  Pressure. 

"Solbrig's  Pliers"  are  the  eldest  machine  of  this  class. 
Upon  one  of  the  beaks,  the  mold  is  placed,  while  the  other 
is  constructed  in  the  form  of  a  shallow  cup  with  an  internal 
diameter  corresponding  to  that  of  the  ring  of  the  mould.  The 
cup  is  filled  with  sheets  of  asbestos  (Section,  Fig.  97),  which 


Fig.  97. 

are  moistened  before  casting.  The  gold  is  fused  directly  upon 
the  mold.  When  the  metal  is  sufficiently  heated  the  pliers 
are  closed,  whereupon  the  steam  generated  by  the  heat  in 
the  moist  asbestos,  drives  the  gold  into  the  mold.  The  sim- 
plicity of  this  principle  makes  the  construction  of  an  inexpen- 
sive apparatus  possible.  In  Europe  this  is  the  type  of  machine 
most  used.  Numerous  machines  of  this  class  are  now  on  the 
market.  The  action  taking  place  in  the  mold  is  the  same 
as  in  the  first  class.  The  pressure  can  not  however  be  deter- 
mined, as  it  is  dependent  upon  three  variable  factors,  the 
amount  of  moisture  contained  in  the  asbestos,  the  temperature 
of  the  metal  and  lastly  upon  the  adaptation  of  the  asbestos 
packing  to  the  edge  of  the  ring  of  the  mold. 


122 

The  pressure  however  varies  in  direct  proposition  to  the 
size  of  the  casting.  "A  pressure  gauge  and  the  regulation  of 
the  pressure  are  quite  superfluous,  since  the  pressure  is  regu- 
lated automatically  by  the  change  of  the  factors  which  enter 
into  the  formation  of  steam.  Thus,  for  a  small  inlay,  owing 
to  the  small  amount  of  metal,  and  the  restricted  quantity  of 
moistened  asbestos  employed,  we  have  less  pressure  than  for 
the  casting  of  a  large  plate,  for  which  we  employ  a  compara- 
tively large  mass  of  fused  metal,  and  large  asbestos  discs  for 
the  production  of  a  greater  volume  of  steam.  The  pressure 
thus  obtained  varies  between  two  and  three  atmospheres."*) 

3.   Pressure  by  Direct  Contact. 

Though  probably  not  the  eldest,  one  of  the  simplest 
machines  of  this  class  is  that  of  Biber  (Pforzheim).    It  con- 


Fig.  98. 

sists  of  a  metal  foot-plate  supporting  a  mold  of  the  usual 
form  (Section,  Fig.  98)  and  a  loosely  fitting  cover  filled  with 
moldine.  The  metal  is  fused  upon  the  mold  and  pressure 
exerted  on  the  wooden  knob  of  the  cover.    The  pressure  in 


*)  0.  Solbrig,  Ash's  Quarterly  Circular,  Jan.   1910. 


123 

the  mold  depends  upon  the  force  used,  and  upon  the  softness 
of  the  moldine.  In  contradistinction  to  class  I  and  II,  the 
pressure  does  not  penetrate  the  investment.  The  force  must 
be  applied  quickly,  as  the  metal  coming  into  contact  with 
the  cold  moldine  solidifies  rapidly.  Solbrig*)  claims  that  "the 
moisture  contained  in  the  substance  employed  (moldine)  is 
the  chief  source  of  the  pressure,  and  for  this  reason  this  kind 
of  press  must  be  put  in  the  class  of  steam  pressure  apparatus." 

4.    Centrifugal  Force. 

But  few  machines  of  this  class  have  appeared  upon  the 
market,  the  first  was  the  Jameson  machine  (Fig.  99).    This 


Fig.  99. 

consists  of  a  circular  casing  attached  to  a  solid  iron  base.  The 
casing  is  divided  by  an  asbestos-covered  plate  into  a  lower 
closed  compartment,  containing  a  spiral  spring  and  a  flywheel, 
and  an  open  compartment  above,  containing  the  casting 
appliance  proper.  A  vertical  axle,  to  which  below  are  attached 
the  spring  and  the  fly-wheel,  carries  at  its  upper  end  short  arms, 

*)  0.  Solbrig,  Cast  Metals  in  Dental  Art,  Asch  Quartly,  Jan.   1910. 


124 

with  movable  holders  for  the  flat  crucibles  and  for  the  molds. 
In  casting,  but  one  mold  is  used,  the  other  serving  as  a  counter- 
weight. Owing  to  the  horizontal  position  of  the  mold,  a  flat 
crucible  lying  opposite  the  sprue  gate  is  used.  A  large  Bunsen 
burner,  for  heating  the  mold,  projects  through  the  asbestos 
plate.  The  walls  of  the  casing  prevent  the  loss  of  gold,  if 
spilled  during  casting.  The  process  of  casting  with  this  machine 
is  the  following:  By  turning  the  arm  8 — 12  times,  depending 
upon  the  amount  of  gold  used,  the  spring  is  wound  up.  The 
brake  a  is  then  set  as  soon  as  the  mould  is  over  the  opening 
of  the  Bunsen  burner.  The  proper  angle  which  the  arm  and 
holder  should  make  to  prevent  spilling,  is  dependent  upon 
the  tension  of  the  spring  and  the  amount  of  gold  used.  After 
rotation  has  begun  the  holder  again  straightens  out.  When 
the  mold  is  sufficiently  hot,  the  gold  is  melted  and  the  brake 
released.  By  centrifugal  force  the  gold  is  thrown  into  the 
sprue-gate  and  into  the  mold. 

As  the  writer  prefers  in  most  cases  to  use  pure  gold  for 
inlays,  and  as  the  crucibles  withstand  a  much  higher  heat 
than  the  investment,  he  employs  oxygen  in  connection  with 
illuminating  gas  to  melt  the  gold  more  rapidly.  The  ordinary 
blow-pipe  is  used,  the  tube  for  the  air  being  connected  with 
the  reducing  valve  of  the  oxygen  cylinder  (Fig.  100).  This 
method  is  cheap  and  efficient,  and  is  of  great  service  in  solder- 
ing platinum  bases  in  porcelain  work. 

On  the  subject  of  pressure  in  the  mold  Price*)  says:  "With 
a  centrifugal  machine  the  actual  effective  pressure  is  the  weight 
of  the  mass  of  molten  gold,  for  our  purpose  irrespective  of 
its  shape,  multiplied  by  the  square  of  the  velocity  of  the  gold 
in  feet  per  second,  divided  by  the  the  radius  in  feet  (not  dia- 
meter) of  the  circle  it  moves  in,  divided  by  32  to  change 
poundal  units  to  pounds  pressure. 

For  example,  if  V2  ounce  of  gold,  which  is  ^/24  pound  troy, 
is  revolving  at  the  rate  of  ten  revolutions  per  second,  which 
is  600  per  minute,  in  a  circle  of  a  diameter  of  ten  inches, 
the  velocity  in  feet  is  10  (diameter)  x  3,14  X  10  (revolutions) 
~  12  (inches)  ^  26,17    feet    per    second,    and    the    pressure 

*)  Items  of  Interest  May  1908. 


125 

V24  pound  multiplied  by  26,17  squared  (the  velocity),  divided 
by  ^/i2  (the  radius  in  feet)  divided  by  32  =  2,14  pounds  actual 
pressure  on  the  inlay," 

Ix  684,86  xfx^2=  2'"- 

"If  the  revolutions  are  twenty  times  per  second,  which  is 
1200  per  minute,  the  actual  effective  pressure  is  8,56  punds. 


M  Arbpifsmanomefer 


J  Inbalhmesspp 


Absperrhahn 


FlaschenvenH) 


Schlauchstutzp 


Flasche 


SicherheifsvGnh 


Fig.  100. 


or  if  only  five  revolutions  per  second  0,53  or  ^/a  pound. 
Remember  the  pressure  increases  as  the  square  of  the  velo- 
city. If  this  pressure  is  on  an  inlay  ^/g  inch  square  ( ^1^^  square 
inch)  it  is  equal 

at    5  revolutions  per  second  to    34^/4  pounds  per  square  inch 


at  10 
at  20 


137 

548 


and  without  decrease  for  back  pressure  or  leakage  as  in  the 
case  of  a  gas  pressure.  If  an  ounce  of  gold  is  used  instead 
of  one-half  ounce  the  pressure  is  double  the  above." 


126 

5.   Pressure  Produced  by  Vacuum. 

This  method  was  first  suggested  by  Frink*).  But  few 
machines  of  this  class  have  been  constructed;  of  these  the 
"Elgin  Vacuum  Casting  Appliance"  is  probably  the  most  per- 
fect (Fig.  101).  This  machine  consists  of  an  iron  tank  containing 
an  exhaust  pump.    Attached  to  the  tank  are  a  gauge  and  an 


Fio-.   101. 


arm  with  two  stop-cocks  and  two  brackets  of  different  size. 
Before  casting,  the  tank  is  exhausted  until  the  gauge  shows 
a  pressure  of  15  units.  The  ring  of  the  mould  must  be  in 
absolute  contact  with  the  bracket.  This  is  tested  by  opening 
the  stop-cock.  The  gage  should  fall  gradually  without  any 
hissing  noise.  When  the  gold,  fused  upon  the  mold,  is  suffi- 
ciently heated,  the  cock  is  opened.  The  metal  is  forced  into 
the  mould  by  atmospheric  pressure. 

*)  Dental  Cosmos  Feb.    1908. 


127 

The  actual  pressure  upon  the  inlay  at  the  moment  of 
casting  may  approximately  be  determined  as  follows.  The 
atmospheric  pressure  .at  thirty  inches  is  14.7  pounds  to 
the  square  inch.  The  gauge  of  the  machine  shows  a  negative 
pressure  of  fifteen  inches,  that  is,  one-half  of  the  normal 
pressure  or  7.35  pounds  to  the  square  inch.  Assuming  the 
cross  sectional  area  of  the  inlay  to  be  Vs  of  an  inch  square, 
or  Vea  of  a  square  inch,  the  effective  pressure  will  then  be  7.35 
X  V64  or  0.115  pound.  No  allowance  is  therein  made  for  leakage 
between  mold  and  bracket,  or  for  the  pressure  penetrating 
the  investment  in  advance  of  the  gold.  The  actually  effective 
pressure  upon  the  inlay  is  therefore  less  than  0.1  pound. 

With  proper  manipulation,  successful  work  can  be  done 
with  machines  of  all  the  classes  described  above,  and  yet,  the 
ideal  machine  has  still  to  be  constructed.  Price  has  suggested 
such  an  apparatus,  in  which  the  pressure  can  be  accurately 
controlled  and  the  temperature  of  the  fused  metal  easily 
determined ;  a  centrifugal  casting  machine,  driven  by  an  electric 
motor,  heated  by  electricity,  and  having  a  pyrometer  attach- 
ment. The  cost  of  a  machine  of  this  kind  would  however  be 
very  great.  For  experimental  work  such  an  apparatus  would 
be  of  the  greatest  value. 

After  casting,  the  mold  should  be  gradually  cooled.  Sudden 
chilling  in  water,  though  advocated  by  many,  is  liable  to  cause 
distortion  through  unequal  contraction  of  the  metal.  When 
the  mold  is  cool,  the  inlay  is  removed  from  the  investment 
and  cleansed  with  a  small  brush.  The  dead-head  is  nipped  off 
at  about  an  eight  inch  from  the  inlay. 

Combination  Inlays. 

A  combination  of  gold  and  porcelain  in  making  inlays  has 
been  advocated  by  a  number  of  writers.  The  use  of  such 
inlays  is  confined  to  the  labial  surfaces  of  anterior  teeth.  The 
results,  in  regard  to  adaptation  are  not  as  satisfactory  as  those 
obtained  with  all-metal  inlays.  In  solidifying  and  in  cooling, 
a  cast  inlay  is  constantly  under  pressure,  if  then  the  inlay 
is  annealed,  as  it  is  in  fusing  the  porcelain,  it  will  undoubtedly 
change  in  form.    Compared  to  a  porcelain  inlay,  its  esthetic 


128 

qualities   are  less   satisfactory.     The   combination  of  a   gold 
inlay  and  silicate  cement  appears  still  more  unesthetic. 

Combination  inlays  are  made  by  cutting  away  a  part  of 
the  metallic  inlay,  and  restoring  the  form  with  porcelain.  To 
avoid  the  difficulty  of  cutting  the  metal,  the  part  to  be  restored 
with  porcelain  is  removed  from  the  wax  model.  This  may  be 
done  with  a  bur,  a  sharp  carving  instrument,  or  with  Roach's 


Fig.   102. 


suction-carver.  The  porcelain  is  either  fused  directly  onto  the 
roughened  inlay,  or  an  impression  is  taken,  and  the  porcelain 
with  the  matrix,  cemented  onto  the  roughened  inlay.  In  this 
method  a  line  of  metal  is  alway  present  between  the  porcelain 
and  the  margin  of  the  cavity. 


Fig.   103. 


Fig.   104. 


The  few  combination  inlays  that  the  writer  has  set,  were 
made  so,  that  no  gold  showed  between  the  porcelain  and  the 
enamel  margin.  As  an  example  a  proximal  cavity  involving 
the  incisal  angle  has  been  chosen  (Fig.  102).  The  general 
cavity-preparation  is  similar  to  that  shown  in  Plate  XIII. 
The  wax-model  is  made  in  the  mouth,  and  into  the  surface, 
visible  in  the  finished  inlay  a  cavity  is  cut  (section  Fig.  103). 
At  the  cutting  edge,  where  the  metal  should  protect  the 
porcelain,  the  wax  is  extended  slighty  beyond  the  normal 
length  (section  Fig.  104).    This  obviates  the  difficulty  of  carv- 


129 

ing  a  feather  edge  upon  the  wax-model.  After  the  porcelain 
has  been  fused  onto  the  inlay,  the  excess  {a,  Fig.  104)  is  care- 
fully removed  with  a  disk,  so  that  no  metal  may  be  visible 
in  the  mouth. 

The  inlay  is  cast  in  22  kar.  gold  and  tried  in  the  cavity. 
It  is  then  removed  and  the  walls  of  the  cavity  which  are  to 
lie  in  contact  with  the  porcelain,  are  covered  with  a  piece 
of  No.  40  gold-foil.  The  foil  should  lie  perfectly  flat,  without 
any  folds,  and  should  extend  slightly  under  the  inlay  (/,  Fig.  105 


Fig.   105. 

At  other  points  upon  the  margin  of  the  cavity,  small  pieces 
of  the  same  foil  are  laid.  This  raises  the  whole  inlay  out  of 
the  cavity  a  distance  equal  to  the  thickness  of  the  foil.  Later, 
when  the  matrix  has  been  stripped  from  the  porcelain,  the 
inlay  again  fits  into  place,  and  the  porcelain  lies  in  absolute 
contact  with  the  walls  of  the  cavity. 

After  the  foil  has  been  properly  placed,  the  inlay  is  in- 
troduced into  the  cavity  and  firmly  held  in  position.  Inlay 
wax  is  then  pressed  into  the  cavity  of  the  inlay  and  against 
the  matrix  (Fig.  105)  which  is  thereby  quickly  and  accurately 
adapted  to  the  margin  of  the  cavity  of  the  tooth.  The  diffi- 
culties often  encountered  in  removing  the  inlay  with  the  matrix 
from  the  cavity,  can  be  overcome  only  by  patient  and  careful 
manipulation.  In  order  to  facilitate  the  removal,  the  sprue 
on  the  inlay  should  be  left  sufficiently  long,  so  that  it  may 
be  firmly  grasped  with  a  pair  of  tweezers.  The  inlay  and 
matrix  are  then  invested,  and  the  contour  restored  with 
Jenkin's  Porcelain  Enamel. 

Another  method  of  combining  gold  and  porcelain  in  an 
inlay,  is  to  make  the  porcelain  part  first,  and  then  to  com- 

Bo decker    Metallic  Inlay.  '     9 


130 

plete  the  metallic  part  of  the  inlay.  The  writer  considers  this 
method  practicable  only  when  large  pieces  of  porcelain  or 
whole  facings  can  be  used  (Plate  VIII). 

The  surface  of  a  metallic  inlay,  after  being  properly  roughen- 
ed, may  be  covered  with  a  layer  of  porcelain.  This,  however, 
is  applicable  only  to  surfaces  not  exposed  to  the  force  of 
mastication. 


Chapter  XI. 
Setting  the  Inlay. 

After  the  inlay  has  been  cast,  all  adherent  particles  of 
investment  material  are  removed  with  a  stiff  tooth-brush  and 
water.  A  perfect  inlay  at  this  stage  should  be  an  exact  repro- 
duction of  the  wax  model.  It  should  have  smooth  surfaces 
with  sharp  margins  and  well  defined  angles.  Before  the  inlay 
is  finally  set  with  cement,  it  must  be  fitted,  burnished,  and 
undercut  or  roughened. 

Fitting  the  Inlay. 

The  excess  metal,  or  dead-head  is  cut  off,  leaving  a  stump 
about  an  eight  of  an  inch  in  length  attached  to  the  inlay. 
In  trying  the  latter  in  the  cavity,  this  stump,  when  not  situated 
at  the  contact  point,  offers  a  convenient  hold  for  the  tweezers, 
while  in  roughening  and  undercutting  the  inlay,  it  can  be 
firmly  grasped  with  a  pair  of  flat-nosed  pliers.  In  cases  where 
the  sprue  has  been  placed  at  the  contact  point,  the  stump 
is  cut  somewhat  shorter.  While  repeatedly  attempting  to 
seat  the  inlay  in  the  cavity,  the  sprue-stump  is  gradually 
ground  down ,  until  with  some  slight  force  the  inlay  is  brought 
into  its  proper  position.  The  contact  point  then  presses  firmly 
against  the  adjoining  tooth.  The  inlay  is  thereupon  removed 
from  the  cavity  and  the  proximal  surface  finished  and  polished 
with  cuttlefish  disks.  Care  should  be  taken  to  touch  the 
contact  point  as  little  as  possible. 

An  inlay,  perfect  in  form,  can  be  introduced  into  the  cavity 
without  difficulty.  If  the  inlay  does  not  go  into  place  easily, 
the  reason  must  be  sought,  and  the  cause  removed.  If  neces- 
sary another  inlay  should  be  made.  The  fact  should  always 
be  borne  in  mind,  that  an  inlay  requiring  much  fitting  can 
never  be  considered  a  perfect  piece  of  work.    If  a  faulty  inlay 


132 

is  set,  the  operator,  and  not  tlie  inlay  process,  is  responsible 
for  any  subsequent  failure. 

An  inlay  may  be  faulty  from  several  causes.  The  sources 
of  error  are:  an  inaccurate  impression,  improper  investment, 
and  imperfections  in  casting.  The  impression  was  distorted, 
if  an  inlay  which  had  been  properly  invested  and  perfectly 
cast,  as  shown  by  its  smooth  surfaces  and  sharp  margins, 
cannot  be  introduced  into  the  cavity.  Either  the  wax  model 
had  changed  in  form,  or  the  thin  anchorage  extenstions  had 
been  bent  in  removing  the  model  from  the  cavity.  If  such 
an  inlay  cannot  be  forced  into  the  cavity,  it  is  far  better 
to  make  another,  than  to  attempt  to  remedy  the  difficulty 
by  grinding.  When  only  the  extensions  are  bent,  the  inlay 
is  firmly  pressed  into  the  cavity  with  a  large  burnisher  and 
the  extensions  driven  into  place  by  means  of  a  smooth  plugger 
upon  which  an  assistant  taps  with  a  mallet. 

Small  rounded  projections,  occurring  in  three  distinct 
forms  upon  the  surface  of  the  inlay,  point  to  the  presence 
of  bubbles  in  the  investment.  A  bubble  directly  upon  the 
surface  of  the  wax  model  results  in  a  hemispherical  projection 
on  the  inlay.  If,  however,  a  very  thin  layer  of  investment 
separates  the  bubble  from  the  wax  model,  the  pressure  in 
casting  will  break  down  this  wall,  and  the  projection  will 
appear  as  an  almost  perfect  sphere  upon  the  inlay.  If  a  number 
of  such  bubbles  lie  together,  the  pressure  will  destroy  not  only 
the  layer  of  investment  separating  the  bubbles  from  the  wax 
model,  but  also  the  walls  between  the  bubbles.  This  gives 
the  projection  upon  the  inlay  an  irregular  form.  The  spherical 
form  can  easily  be  removed  with  a  sharp  instrument.  The 
other  forms  can  be  removed  only  by  grinding.  If  present  in 
greater  numbers,  especially  at  or  near  the  margin  of  the  cavity, 
they  are  apt  to  make  the  inlay  worthless. 

An  imperfectly  cast  inlay  may  be  faulty  in  three  respects ; 
it  may  shov/  either  a  granular  surface,  rounded  margins,  or 
blow-holes.  The  granular  surface  results  from  the  use  of  super- 
heated metal  in  casting.  If  the  mould  made  of  investment 
material  had  the  same  physical  properties  as  one  made  of 
metal,   overheating  the  gold  would  have  no  influence  upon 


133 

the  exact  size  of  the  inlay.  Overheated  metal  (h,  Fig.  106) 
cast  in  a  metallic  mold  (a),  shows  a  smooth  surface  with  slight 
depressions.  In  number,  the  latter  depend  on  the  degree  to 
which  the  metal  has  been  overheated,  and  upon  the  mass  of 
the  metal  itself.  The  size  of  the  casting  is  in  no  way  altered. 
If,  however,  an  investment  material  is  used  in  making  the  mold. 


/CI 


Fis.   106. 


Fig.   107. 


the  high  heat  of  the  metal  {h,  Fig.  107),  destroys  the  smooth- 
ness of  the  walls  of  the  mold  (a),  thereby  producing  slight 
elevations  and  depressions  which  give  the  surface  of  the  metal 
a  granular  appearance.  The  size  of  the  casting  is  somewhat 
increased.  It  is  not  necessary  to  call  further  attention  to  the 
significance  of  this  fact  in  casting  inlays. 

The  damage  done  by  the  overheated  metal  is  sometimes 
confined  to  the  wall  lying  opposite  the  sprue-gate.  In  such 
cases,  the  metal  though  not  greatly  overheated,  is  sufficiently 
hot  to  disintegrate  the  surface  of  the  investment  where  it  first 
strikes  the  wall  of  the  mold.  The  current  of  the  molten  metal 
then  erodes  the  surface  at  this  point.    It  is  preferable,  there- 


134 

fore,  that  the  point  opposite  the  sprue-gate  should  he  upon 
a  smooth  wall,  and  not  near  the  margin  of  the  inlay,  or  near 
the  angles  of  an  anchorage  extension.  The  sharp  angle  of  the 
occlusal  step  at  the  axial  wall,  is  therefore  an  unnecessary 
source  of  danger  which  should  be  avoided  by  sloping  this  part 
of  the  cavity,  as  shown  in  Plate  I.  As  the  point  of  attachment 
is  determined  by  the  contact  point,  the  direction  of  the  current 
of  metal  may  be  varied,  by  altering  the  angle  at  which  the 
wax  model  is  set  upon  the  sprue. 

Overheating  the  metal  in  casting,  often  makes  the  inlay 
worthless.  Especially  is  this  true  of  inlays  having  complex 
anchorage  extensions;  as  for  example,  a  proximal  inlay  with 
transverse  fissure  anchorage  in  a  lower  molar  (Plate  I).  At  the 
angles,  where  the  longitudinal  and  transverse  fissures  cross 
each  other,  the  current  of  overheated  metal  distintegrates  the 
investment  and  carries  away  the  loosened  particles.  Under 
such  circumstances,  the  finished  inlay  cannot  possibly  fit  into 
the  cavity. 

The  only  means  of  fitting  an  inlay,  with  a  partially  or 
totally  granular  surface,  is  by  careful  grinding.  A  perfect 
result  is,  however,  rarely  obtained.  If  the  defect  is  confined 
to  a  small  area,  the  following  method  may  be  tried.  The 
inlay  is  placed  in  the  cavity  and  rocked  back  and  forth  under 
pressure.  Upon  examining  the  under  surface  of  the  inlay, 
burnished  spots  will  be  found  which  mark  the  places  where 
the  inlay  rests  upon  the  tooth.  The  amount  of  metal  to  be 
removed  must  be  determined  beforehand,  as  a  second  attempt 
to  locate  the  point  of  difficulty  by  rocking  the  inlay  will 
usually  be  unsuccessful,  the  burnished  spots  not  being  recogniz- 
able upon  the  ground  surface  of  the  metal.  If  further  efforts 
to  fit  the  inlay  are  to  be  made,  the  walls  of  the  cavity  should 
be  coated  with  coloring  matter.  The  inlay  can  then  be  re- 
peatedly tried  in  the  cavity,  and  the  places  marked,  ground  off. 
This  procedure  cannot,  however,  be  recommended  by  the  writer, 
as  the  result  always  is  an  imperfect  piece  of  work.  In  the 
time  spent  in  attempting  to  fit  a  faulty  inlay,  another  wax 
model  can  be  made.  And  the  finished  inlay  will  then  be  far 
more  satisfactory. 


135 


Rounded  margins  (Fig.  108)  are  the  result  of  an  insuffi- 
cient heating  of  the  metal  in  casting.  Whether  the  faulty 
inlay  can  be  used  or  not,  depends  upon  the  degree  of  the 
defect  and  upon  the  position  of  the  cavity  to  be  filled.  An 
inlay  with  slightly  rounded  margins,  in  a  simple,  easily  access- 
ible cavity,  can  by  burnishing,  be  perfectly  adapted  to  the 
margins.  On  the  other  hand,  a  proximal  inlay  with  edges 
equally  rounded  is  worthless,  as  the  cervical  margin  of  the 
cavity  is  not  sufficiently  accessible.  A  proximal  inlay  must 
therefore  always  be  perfect  in  this  respect. 

For  the  purpose  of  adapting  the  rounded  edges  of  the 
inlay  to  the  margins  of  the  cavity,  the  corrugated  burnisher. 


i 


Fig.   108. 


Fig.   109. 


Fig.   110. 


also  called  tomato-burnisher,  is  the  most  suitable  instrument. 
The  burnisher,  rotating  in  the  direction  of  the  margin  {a.  Fig.  109) 
throws  up  a  ridge  at  this  point.  The  purer  the  gold,  the  more 
easily  can  this  be  accomplished.  If  the  extreme  edge  of  the 
enamel  is  at  right-angles  to  the  surface  of  the  tooth,  there 
still  remains  a  space  at  h  (Fig.  109)  after  the  burnishing  has 
been  completed.  Further  burnishing  will  not  obliterate  this 
space,  but  will  only  force  the  metal  over  the  edge  of  the 
enamel  (Fig.  110).  If  the  margin  of  the  enamel  is  bevelled 
(Fig,  111),  the  gold  can  be  more  easily  adapted  (Fig.  112). 
Adapting  the  slightly  rounded  edges  of  a  faulty  inlay  by 
burnishing,  is  therefore  permissable  only  in  simple  cavities 
with  bevelled  enamel  margins.  Upon  an  occlusal  surface,  where 
the  walls  of  the  cavity  have  been  prepared  at  right- angles  to 
the  surface,  such  a  procedure  cannot  be  recommended,  as  at 
this  point  a  perfect  adaptation,  extending  well  towards  the 


136 

floor  of  the  cavity  is  absolutely  essential.  An  inlay  with 
rounded  margins  should,  never  be  set  in  an  occlusal  cavity 
unless  deep  fissures  have  been  carved  into  this  surface. 

Blow-holes  can  be  repaired  only  by  filling  the  defect  with 
gold  foil.  If  the  hole  has  resulted  from  the  presence  of  foreign 
matter,  the  inlay  should  be  boiled  in  acid.  The  form  of  the 
defect  is  usually  such,  that  it  offers  ample  retention  for  the 
filling.  Should  this  not  be  the  case,  undercuts  must  be  made 
in  the  inlay. 

When  the  inlay  fits  into  the  cavity,  the  bite  should  be 
controlled.    If  the  inlay  is  too  high,  this  may  be  corrected 


Fig.   HI. 


Fig.   112. 


by  allowing  the  patient  to  bite  upon  tracing-paper,  and  grind- 
ing away  the  places  marked  until  the  articulation  is  correct. 
The  edges  of  the  inlay  are  then  burnished  against  the  margins 
of  the  cavity,  upon  the  occlusal  surface  with  a  corrugated 
burnisher,  and  on  the  proximal  surface  with  a  flat  hand- 
burnisher. 

In  removing  the  inlay  from  the  cavity,  care  must  be  taken 
to  avoid  injuring  the  edges.  Occluso-proximal  inlays  should 
be  removed  by  placing  the  point  of  an  instrument  below 
the  contact  point  and  pressing  in  the  direction  of  the  occlusal 
surface.  In  simple  cavities  it  is  often  difficult  to  remove  the 
inlay  without  injuring  the  edge.  This  danger  may  be  avoided 
by  leaving  the  stump  of  the  sprue  attached  to  the  inlay  until 
after  it  has  been  burnished.  As  the  sprue-stump  interferes 
at  certain  points,  special  attention  should  be  paid  to  these 
in  reburnishing  the  inlay  after  it  has  been  introduced  into 
the  cavity,  and  before  the  cement  has  set. 


137 

Undercutting  and  Roughening  the  Inlay. 

The  inlay,  at  this  stage,  is  ready  to  be  undercut  or 
roughened.  Simple  inlays,  firmly  held  with  flatnosed  pliers 
by  the  sprue -stump,  may  be  easily  undercut  with  a  fine 
hand -saw.    If  the  sprue -stump  has  previously  been  cut  off. 


■ 

■■ 

^^^^^^^B 

■j 

H 

B 

Ml 

o   fl 

B  • 

K 

1^^ 

B^ 

^^H 

1 

li; 

f^ri 

1 

m      '-^ 

1 

p  1 

Fig.   113. 

or  if  the  inlay  is  of  complex  from,  it  must  be  held  in  the 
fingers,  and  the  undercuts  made  with  a  small  knife-edged 
stone,  or  a  crown  saw  in  the  dental  engine.  The  rotary  saw, 
though  useful,  cannot  be  recommended,  it  being  liable  to  jump 
over  the  edge  of  the  inlay  and  injure  the  fingers.  As  cutting 
the  metal  always  leaves  feather-edges,  these  must  be  ground 


138 


3 


Fio.   114. 


off  from  the  margins  of  the  un- 
dercuts, and  the  inlay  again  tried 
in  the  cavity.  If  the  size  of  the 
inlay  permits,  it  is  always  pre- 
ferable to  make  the  necessary  un- 
dercuts in  the  wax  model. 

The  best  instrument  for  rough- 
ening inlays  is,  in  the  opinion  of 
the  writer,  the  mechanical  engrav- 
ing apparatus  shown  in  Fig.  113. 
It  is  known  in  the  German  jewel- 
lers' trade,  as  the  dot-engraving  ap- 
paratus Matador  ( Gravier-Punk- 
tierapparat  Matador).  It  consists 
of  a  clockwork  which  drives  a 
hinged  weight  {a),  and  a  counter- 
weight (6).  Only  the  former  strikes 
'^^Sillll  the  end  of  the  engraving  instru- 

ment. As  the  weight  is  usually 
not  heavy  enough,  a  small  piece 
of  lead  must  be  screwed  onto  the 
upper  surface.  Owing  to  the  fact 
that  the  weight  is  hinged,  the  blow 
given  by  this  instrument  is  per- 
fectly "dead".  The  Bonwill  mal- 
let*), depending  for  its  action  upon 
an  immovable  cam,  carried  on  a 
wheel  and  stricking  the  end  of  the 
instrument  at  each  revolution, 
gives  a  short,  sharp  blow.  As  the 
gold,  in  this  case,  has  not  sufficient 
time  to  escape,  the  surface  is  but 
slightly  roughened.  With  the 
Bonwill  mallet  the  point  of  the 
instrument,  should  be  small  and 
very  sharp,   while  with   the    en- 

*)  G.  S.  Hersey,  Dental  Cosmos  Nov. 
1906,  p.  1167. 


189 

graving  apparatus   the  point  should  be  ground  in  the  form 
of  a  half-round  chisel. 

At  points  where  nothing  has  been  removed  from  either 
wax  model,  inlay,  or  cavity  wall,  the  inlay  is  roughened  by 
blows  at  right-angles  to  the  surface  (Fig.  13).  But  where  the 
space  between  inlay  and  cavity  wall  permits,  the  step-like 
projections  (Fig.  14),  made  be  applying  the  roughening  instru- 
ment obliquely,  are  to  be  preferred. 

In  the  tooth,  the  undercuts  should  be  placed  and  shaped 
as  has  been  described  under  "Retention"  (Chaps.  Ill  and  IV). 
The  removal  of  the  last  traces  of  caries,  or  of  the  material 
filling  the  natural  undercuts,  often  makes  further  undercutting 
unnecessary. 

The  Cement. 

Before  discussing  the  subject  of  setting  the  inlay,  the 
requisite  qualities  of  a  cement  for  this  purpose  will  be  men- 
tioned.   The  material  used  as  an  inlay  cement  should, 

1.  be  so  fine  grained,  that  it  forms  a  very  thin  film  under 
pressure, 

2.  possess  great  compression  strength, 

3.  neither  expand  nor  contract  during  the  process  of  setting, 

4.  be  impenetrable  to  moisture, 

5.  possess  hydraulic  qualities, 

6.  set  sufficiently  rapidly, 

7.  be  as  insoluble  as  possible,  and 

8.  possess  adhesive  qualities. 

Of  these  qualities  the  first  four  are  essential,  while  the 
last  four  add  to  the  value  of  the  cement. 

1.  Experiments  to  determine  the  relative  value  of  cements, 
in  regard  to  all  the  above  mentioned  qualities,  have  not  yet 
been  made.  Joseph  Head  (Philadelphia)  published  an  article*) 
upon  thickness  of  the  cement  line,  and  as  the  result  of  his 
experiments,  tabulated  below,  comes  to  the  following  con- 
clusions. The  thickness  of  the  cement  layer  depends  upon 
the  size  of  the  cement  grains.  Great,  or  prolonged  pressure 
changes  the  result  but  little. 


^)  Tests  on  the  Inlay  Cement  Problem.     Dental  Cosmos,  July  1905. 


140 


8  poundsl), 
1  Min. 

8  pounds 
until 
set. 

25  pounds, 
1  Min. 

25  pounds 
until 
set. 

50  pounds, 
1  Min. 

50  pounds 
until      . 
set. 

lOOpounds, 
1  Min. 

100  pounds 
until 
set. 

Harvard  (coarse) 

.002433) 

.00249 

,,         Inlay 

(Jenkins) 

.00168 

.00171 

,,         Special 

(Head) 

.00156 

.00152 

.00143 

.00125 

.00106 

001175 

.00114 

.00089 

Ames  Inlav  .   .  . 

.00109 

.00096 

.000886 

.000882 

.000725 

.000702 

.00079 

.000604 

Ash 

.00229 

Harvard   Pulv.  2) 

.00033) 

.00027 

1)  Pressure  on  ^/4  square  inch. 

2)  Harvard  Pulv.  is  a  Harvard  cement  "pulverized  in  an  agate  mortar 
until  the  grit  was  imperceptible  to  the  teeth". 

3)  Thickness  of  film,  in  fractions  of  an  inch.  (The  tMckness  of  No.  30 
gold  foil  is  about  .0003  in.) 

2.  Experiments  to  determine  the  compression  strength  of 
the  various  oxyphosphate  cements,  have  not  been  made. 

3.  und  4.  The  second  table,  compiled  from  the  article  of 
G.  C.  Poundstone*)  (Chicago),  shows  the  structure,  the  expan- 
sion, and  the  permeability  of  a  number  of  cements.  The  names 
of  the  preparations  are,  however,  not  mentioned. 

5.  A  hydraulic  cement  is  one  which  sets  under  water. 
It  has  been  claimed,  that  oxyphosphate  cements  are  not 
hydraulic,  that  they  are  only  apparently  so,  owing  to  the 
rapidity  with  which  they  set.  Only  by  practical  tests  can  this 
question  be  decided. 

6.  The  rapidity  with  which  a  cement  should  set,  depends 
upon  personal  preference  and  upon  the  difficulty  of  introducing 
the  inlay  into  the  cavity.  With  every  cement,  the  time  of 
setting  can  be  regulated  by  varying  the  relative  amounts  of 
the  liquid  and  the  powder,  or  by  using  powders  containing 
more  or  less  coloring  matter.  Some  manufacturers  recommend 
the  use  of  a  retarding  "flux". 

7.  All  cements  are  more  or  less  soluble  in  the  mouth.  The 
solubility  of  any  of  the  standard  preparations  is,  however,  not  so 
great  as  to  endanger  the  durability  of  a  perfectly  adapted  inlay. 

8.  In  the  retention  of  an  inlay,  other  factors  are  far  more 
important   than   mere    adhesiveness    of   the   cement.     While 

*)  The  Cement  Problem  in  Inlay  Work.     Cosmos,  July  1905. 


141 


o. 

5 

TO 

1' 

_g 

set  under 
een  etched 
s,    and   pi 
I  eosin. 
3  penetrat 

CO 

73 

to 

t3 
1—1 

1 

T3 

CO 

c/: 

o 

lO 

t3 

o 

-i 

CO 

CO 

'S    .^."^ 

-* 

:  e:  ¥  .5  -e 

1 

-ti 

1 

-^ 

1 

1 

CO      1^  "f* 

1 

nent, 
glass 
niple 

1 

-ti 

1 

^ 

lO 

o 

^  •'     >  1—1 

O 
I— 1 

6  i  S3      ^ 

m 

m 

0 

<b          i) 

0) 

2  c 

CO    cj    CO    t3 

M     S 

-4^ 

c 

^  o 

c3    5    ce    o 

^  S 

o 

<U  .w 

OJ    .S        Oj     •-! 

Oj  .-I 

1  a 

a  a 

:g-i 

Oi 

o 

;.<    CO 

o 

QJ 

0) 

tj     CC     t.     CO 

o  c  o  c2 

■^   m 
o    C 

bxj  ^ 

fl 

fi 

S    eS 

a 

d 

c 

c  ce  c  rt 

.a  ^ 

Oj      d 

.^ir  eg 

o 

o 

'        Q-i 

o 

o 

o 

•-I    ^  --H    r^ 

,Q     O 

S   g- 

^ 

^ 

-p  y, 

^ 

^ 

^ 

^    (T-P    X 

-n.  ?r 

■g 

r^       <t> 

^   a,  ^  0) 

^     (U 

02 

H 

CO  " 

, 

s_ 

±. 

rL 

i. 

s 

s^ 

s. 

d,       d. 

d. 

><     g     o 

O 

o 

c^ 

^ 

O 

-* 

o 

T-i         -l^ 

c» 

I—I       p^      cfl 

(r<i 

C<I 

b^l 

E2 

rL 

d- 

i 

i 

i. 

rL 

d. 

d-        d. 

d. 

fii 

I— ( 

co 

■* 

lO 

t- 

-* 

(^5 

C-         lO 

CO 

(M 

'^ 

-* 

(>J 

(M 

CO 

^ 

(M         CO 

CO 

.2o 

S 

T— 1 

CO 

O 

d. 

CO         ^ 

lO 

s 

(M 

G^ 

(M 

C<) 

C<l 

CO 

CO 

cq       CO 

CM 

>, 

^ 

C 

a 

^ 

Bubblei 

in 
setting 

^ 

s 

1"  i 

t> 

> 

4) 

So 

0)     « 

,__, 

O 

1— H 

^ 

,__, 

<D 

a:) 

»— 1          I—* 

© 

S^ 

'& 

a" 

Is 

^ 

'3 

^ 

^ 

le      '3 

^1 

a 

g 

>i 

a 

a    a 

XJl 

H^l 

CO 

lU 

CZ2 

h^l 

i-:i 

02        OQ 

l-i 

> 

rL 

d- 

d. 

i 

d- 

d. 

d. 

d-       d. 

d. 

§     « 

lO 

lO 

lO 

CX> 

lO 

o 

(r5 

o       lo 

lO 

(D 

S   2 

T-H 

i-H 

I— ( 

1—1 

1—1 

CO 

o-j 

(M         —1 

1— < 

3 

1 

1 

1 

1 

1 

1 

1 

1             1 

1 

s 

< 

00 

o 

c- 

(M 

o 

CO 

CX) 

lO       o 

00 

t-l 

o  - 

1—1 

'-' 

'-* 

"-^ 

■— ' 

"— ' 

>:, 

>> 

>> 

s 

fl 

fl 

fl 

>  fe 

>^ 

t^ 

>> 

> 

a 

;>> 

>. 

c    a 

ce 

a 

s 

:p  ^ 

a 

1=1 

fl 

ca    g 

b 

ce 

t 

o 

0) 

<s 

> 

> 

> 

<U               <D 

'd- 

:L 

:±. 

d- 

d. 

d- 

d. 

d.       d- 

d- 

m 

.2  "S  £? 

lO 

O 

O 

CO 

lO 

CO 

CO 

o      c- 

lO 

,2 

r^O 

LO 

lO 

lO 

(M 

lO 

^ 

'^         C^I 

CM 

^ 

^ 

^ 

^ 

2   ir! 

D 

OJ 

® 

0) 

3 

:§  .S 

^ 

^ 

^ 

<4H 

^ 

^ 

^    ^ 

=« 

0) 

b 

>> 

h1 

rt    S 

s 

<D 

<u 

03 

!> 

> 

> 

> 

a 

-^i 

CQ 

d 

Q 

&i 

fa' 

d 

W     ^' 

^ 

142 

cement  is  still  very  soft,  it  undoubtedly  is  "sticky",  but  after 
it  has  set,  it  does  not  possess  any  adhesive  qualities.  The  fact 
that  old  cement  can  often  be  removed  only  with  difficulty 
from  the  walls  of  the  cavity,  does  not  prove  the  adhesiveness 
of  cement,  but  proves  that  the  cement  was  of  such  a  character, 
that  it  could  adapt  itself  to  the  most  minute  inequalities  upon 
the  surface  of  the  dentine.  The  tests  made  to  determine  the 
adhesiveness  of  cements  are  of  little  practical  value,  as  they 
do  not  reproduce  the  conditions  existing  in  the  cavity  of  the 
tooth,  while  in  the  mouth.  Poundstone  tested  the  cements 
A  to  J,  by  cementing  together  ivory  blocks  whose  surfaces, 
60  square  millimeters  in  area,  were  roughened  with  a  vul- 
canite file.  "They  were  kept  dry  for  24  hours,  when  they 
were  pulled  apart."  The  average  force  required  varied  from 
231/2 — 59  V4  pounds.  From  a  practical  stand  point  the  follow- 
ing tests  are  of  interest.  "Repeated  tests  were  made  by 
cementing  the  blocks  together  and  keeping  them  in  saliva 
in  the  incubator  at  37  °  C,  but  in  every  instance  the  force 
necessary  to  separate  them  was  so  slight  that  it  was  impossible 
to  measure  it  with  any  degree  of  accuracy.  These  were  flat 
surfaces,  with  force  applied  perpendicular  to  the  surface.  When 
force  was  applied  parallel  with  the  surface,  i.  e.  when  an  attempt 
was  made  to  slide  the  blocks  apart,  considerable  resistance 
was  met  with,  the  film  of  cement  apparently  interlocking  into 
the  uneven  surfaces  of  the  blocks  on  either  side." 

The  constant  improvements  made  by  the  manufacturers, 
make  it  impossible  to  state  which  cement  most  completely 
fulfills  the  requirements  mentioned  above.  Each  operator 
must  be  guided  by  his  own  experience,  in  selecting  an  inlay 
cement.     Only  standard  preparations  should  be  considered. 

Drying  the  Cavity. 

The  use  of  the  rubber  dam  is  not  necessary  in  setting  an 
inlay.  The  process  occupies  but  so  short  a  time,  that  the  field 
of  operation  can  usually  be  kept  dry  very  easily.  In  two  to 
three  minutes  after  the  first  drying  of  the  cavity,  the  inlay 
may  safely  be  exposed  to  the  saliva,  if  a  hydraulic  cement, 
mixed  by  an  assistant,  has  been  used. 


143 

To  keep  the  tooth  dry,  the  usual  appUances  are  employed. 
As  these  are  well  known  they  need  not  be  described  in  detail. 
Cotton  rolls,  or  napkins  in  connection  with  ordinary  or  specially 
constructed  clamps,  tongue-holders,  or  mouth  -  specula  are 
most  commonly  used.   The  saliva-pump,  also  is  of  great  value. 

The  tooth  is  cleansed  with  a  stream  of  water,  and  the 
cotton  rolls  put  in  position.  The  cavity  is  then  dried  and 
disinfected.  For  this  purpose  a  variety  of  medicaments  are 
used.  The  method  of  the  writer  is  the  following.  A  pledget 
of  cotton  saturated  with  a  solution  of  equal  parts  of  sodium 
hypchloride  (NaClO)  and  potassium  hypobromide  (KBrO)  is 
placed  in  the  cavity.  If  the  dentine  is  sensitive,  the  wet  cotton 
is  warmed  over  the  flame  of  an  alcohol  lamp.  With  a  broach, 
around  which  a  few  fibers  of  cotton  have  been  wrapped, 
dilute  sulphuric  acid  is  added  until  the  reaction  ceases.  The 
reaction  which  take  place,  consists  in  a  liberation  of  chlorine, 
bromine  and  oxygen.  As  these  are  present  in  their  nascent 
state,  they  have  a  powerful  germicidal  action,  thus  thoroughly 
disinfecting  the  tooth.  The  cavity  is  then  again  flooded  with 
the  above-mentioned  alkaline  solution,  to  neutralize  every  trace 
of  the  acid,  and  is  dried,  without  being  again  rinsed  out  with 
water.  Even  the  most  sensitive  dentine  can  be  disinfected, 
if  the  solutions  are  used  in  the  order  mentioned,  and  care- 
fully warmed.  Experience  has  shown,  that  as  a  result  of  this 
procedure  the  cement  forms  a  strong  attachment,  probably 
owing  to  the  the  action  of  the  acid  in  roughening  the  surface 
of  the  dentine. 

Regarding  the  much  debated  question  of  thoroughly  drying 
the  cavity,  the  writer,  from  practical  experience,  believes  a 
dry  surface  to  be  not  alone  desirable  but  absolutely  necessary 
for  a  perfect  union  between  cement  and  dentine.  W.  V.  B.  Ames"^), 
however,  states:  "I  believe  that  it  is  thoroughly  impractical 
and  unscientific  to  expect  to  be  able  to  flow  a  proper  mix 
of  cement  to  this  desiccated  surface  and  have  it  give  the 
maximum  of  adhesion,  because  this  cement  will  simply  bridge 
across  the  microscopical  irregularities  of  this  surface,  and  the 
tubuli  —  if  you  please  —  without  knitting  into  them,  as  the 

*)  Dental  Summarv  Vol.  XXV,  Xo.  1   p.  71. 


144 

cement  must  to  give  maximum,  adhesion.  Granting  that 
thorough  cleansing  and  superficial  desiccation  is  desirable, 
I  will  claim  that  we  should  then  thoroughly  moisten  this 
surface  with  the  liquid  of  the  cement  we  are  about  to  use, 
or  possibly  better,  some  plain  syrupy  phosphoric  acid,  and 
after  being  satisfied  that  this  has  caused  the  displacement  of 
air  in  all  inequalities  of  the  surface,  all  visible  surplus  of  this 
should  be  removed  by  air  blast  or  absorbents."  Only  by 
making  a  series  of  comparative  tests,  can  this  question  be 
decided.  The  writer,  however,  believes,  that  the  thinly  mixed 
cement,  under  the  pressure  of  forcing  the  inlay  into  place, 
can  more  readily  fill  out  all  minute  depressions  if  these  are 
empty,  than  if  they  have  previously  been  filled  with  another 
fluid. 

With  absolute  alcohol  and  hot  air  the  cavity  is  dried.  If  the 
dentine  is  sensitive,  the  pledget  of  cotton  saturated  with 
alcohol  is  ignited  and  allowed  to  burn  5 — 10  seconds.  After 
being  extinguished,  it  is  immediately  placed  in  the  cavity, 
and  the  alcohol  partially  evaporated  with  the  hot  air  syringe. 
Thereupon  the  cotton  is  removed,  and  the  drying  of  the  den- 
tine continued  until  its  surface  becomes  white.  After  about 
a  minute  the  whiteness  disappears,  proving  that  the  dentine 
had  been  dried  out  but  superficially,  and  that  it  rapidly  regains 
its  normal  moisture.  This  is  of  advantage  to  the  hydraulic 
cement  in  setting. 

Setting  the  Inlay. 

General  directions  for  mixing  the  inlay  cement  cannot 
be  given,  as  each  preparation  requires  special  handling, 
and  this  can  only  be  determined  by  practical  tests.  With 
the  cement  mixed  to  the  proper  consistency  the  walls  of 
the  cavity  are  carefully  covered.  The  dentine  should  be  cov- 
ered at  every  point,  to  avoid  the  danger  of  imprisoning 
air  under  the  inlay.  The  air  forms  a  cushion,  which  drives 
the  inlay  out  of  the  cavity  before  the  cement  has  set,  or 
it  may  escape  partially  and  leave  a  space  between  the  in- 
lay and  the  wall  near,  or  at  the  margin  of  the  cavity.  The 
thin  cement,  to  cover  the  walls  of  the  cavity,  is  taken  up  on 


145 

the  point  of  a  spatula  and  dripped  into  the  cavity  if  the  tooth 
is  in  the  lower  jaw.  If  it  is  in  the  upper,  the  spatula  is  held 
before  the  opening  of  the  cavity  and  the  cement  pushed  in 
with  a  large  ball-burnisher.  With  a  smaller  instrument  it  is 
then  quickly  spread  over  the  surface  of  the  dentine,  and  an 
additional  quantity  of  cement  introduced  into  the  cavity. 
With  a  pair  of  tweezers,  preferably  those  suggested  by  A.  Gutt- 
mann  (Berlin)  for  porcelain  inlays  (Fig.  115)  as  they  prevent 
the  inlay  from  escaping  from  between  the  points,  the  inlay 
is  placed  in  the  cavity.     By  alternately  pressing  with  two 


Fig.   115. 

burnishers,  the  inlay  is  forced  into  place  with  a  rocking  motion 
(Taggart).  This  seats  the  inlay  more  quickly  and  dislodges 
the  larger  granules  of  cement  more  easily  than  steady  pressure 
in  one  direction. 

After  the  inlay  is  in  position  the  margins  are  rapidly  bur- 
nished and  steady  pressure  is  exerted  for  about  one  minute. 
With  an  explorer  the  margins  are  then  examined.  If  at  any 
place  the  inlay  protrudes  slightly,  though  this  should  not 
happen  in  a  perfect  piece  of  work,  the  cement,  still  somewhat 
soft,  is  removed  at  that  point  with  a  fine  instrument,  so  that 
later  the  metal  can  be  burnished  against  the  margin  of  the 
cavity.  As  moisture  can  now  no  longer  affect  the  hydraulic 
cement,  the  cotton  rolls  may  be  removed.  The  patient  should 
be  cautioned  not  to  occlude  tightly,  as  the  cement  only  sets 
in  8 — 10  minutes.  The  surplus  cement  should  remain  in  place 
until  it  has  hardened. 

Finishing  and  Polishing  the  Inlay. 

When  the  cement  has  set,  the  excess  is  chipped  off  with 
a  sharp  instrument.    This,  by  the  way,  would  not  be  possible 

Bo  decker,  Metallic  Inlay.  10 


146 

if  the  cement  were  truly  adhesive.  With  tracing-paper  the 
bite  is  controlled.  If  it  proves  to  be  too  high,  —  a  serious 
matter  if  the  inlay  was  of  the  proper  height  when  previously 
tried  in  the  cavity,  —  the  place  marked  must  be  ground  off 
with  a  small  stone  (Fig.  116),  or  with  a  plug  finishing  bur. 
Care  should  always  be  taken,  when  grinding  near  the  edge  of 
the  inlay,  to  let  the  instrument  rotate  so,  that  the  gold  is 
forced  against  the  margin  of  the  cavity.  For  this  reason,  it 
is  necessary  to  have  left-as  well  as  right-cut  finishing  burs 
on  hand.  The  pear-shaped  form  is  the  most  serviceable  (Fig.  117). 
These  instruments  being  small,  confine  there  action  to  a  limited 


Fiff.   116. 


lig.   117. 


Fig.   118. 


Fig.   1L9. 


area.  They  cut  more  rapidly  than  the  gem-points,  as  long  as 
they  are  sharp.  The  double  cone-shaped  bur  (Fig.  118)  is  used 
to  restore  the  form  of  the  fissures  that  has  been  destroyed 
in  grinding  the  inlay.  The  margins  of  the  occlusal  surface 
are  flushed  with  fine  stones. 

After  the  bite  has  been  corrected,  the  margins  of  the 
proximal  cavity  should  be  examined.  If  the  unpleasant  dis- 
covery is  made,  that  the  inlay  protrudes  from  the  cavity, 
the  edges  must  be  ground  down,  preferably  with  spear-shaped 
finishing  burs  (Fig.  119).  At  accessible  places  a  somewhat 
thicker  form  may  be  used,  as  this  does  not  become  dull  so 
rapidly.  As  the  metal  should  always  be  cut  in  the  direction 
of  the  cervical  margin,  right-  and  left-cut  finishing  burs  are 
required.  In  most  cases  it  will  be  necessary  to  use  them  in 
the  right- angle  handpiece.  Where  there  is  no  danger  of  in- 
juring the  contact  point,  sandpaper  disks  may  be  employed. 
Great  care  should  be  exercised  in  finishing  the  proximal 
margins,  as  there  is  always  danger  of  dislodging  the  newly 


147 

set  inlay  by  pressure  upon  this  surface.  It  is  better  therefore, 
to  postpone  any  extensive  operation  of  this  kind  until  a  sub- 
sequent sitting. 

The  writer  is  not  able  to  appreciate  the  beauty  of  a  high 
polish,  prefering  a  smooth  but  dull  surface,  which  makes  a 
metallic  filling  less  conspicuous.  The  inlay  is  quickly  polished 
by  using  rubber  or  moose-hide  disks,  and  cloth  strips  with 
a  mixture  of  carborundum  flour  and  vaseline.  The  action  is 
rapid  and  the  effect  very  satisfactory. 


10* 


Chapter  XII. 
The  Metallic  Inlay  as  a  Bridge  Abutment. 

Owing  to  its  massiveness  and  apparent  strength,  the  metaUic 
inlay  has  appealed  to  many  as  a  means  of  anchoring  bridges. 
Various  forms  of  inlay  bridge  abutments  have  been  suggested, 
but  the  majority  of  these  fail  when  put  to  a  practical  test. 
Many  men,  therefore  condemn  the  use  of  the  inlay  abutment. 
Nevertheless  it  remains  a  fact,  that  inlays  have  been  used 
successfully  for  this  purpose,  and  that  if  properly  constructed 
in  accordance  with  certain  definite  mechanical  principles,  they 
may  certainly  be  used  with  safety  in  some  cases. 

It  is  not  the  intention  of  the  writer  to  suggest  still  another 
form  of  inlay  abutment,  but  only  to  describe  the  mechanical 
principles  that  must  be  taken  into  account  in  the  construction 
of  an  inlay  of  this  kind. 

In  explaining  the  stress  and  strain  upon  an  inlay  used  as 
a  filling,  only  the  force  of  mastication  was  considered,  while 
movement  of  the  individual  tooth  was  disregarded.  This  move- 
ment, however,  becomes  of  prime  importance  in  determining 
the  form  of  the  inlay  abutment.  To  the  mechanical  factors 
to  be  considered  in  constructing  an  ordinary  inlay,  must  be 
added  that  of  movement  of  the  tooth  in  three  directions; 
bucco-lingually,  mesio-distally,  and  vertically.  The  effects  of 
these  movements  on  inlay  abutments  situated  in  bicuspids 
and  molars  will  be  described  in  detail.  For  the  sake  of  clearness, 
a  bridge  with  but  one  inlay  abutment  has  been  chosen  as  an 
example.  The  inlay  is  placed  in  the  second  molar,  while  the 
other  abutment  consists  of  a  shell-crown  placed  upon  the 
second  bicuspid.  A  square  bar  connecting  the  two,  represents 
the  bridge. 

Bucco-lingual  Movement  of  the  Anchor  Teeth. 

Movement  in  the  bucco-lingual  direction  will  not  endanger 
the  anchorage  as  long  as  both  abutment  teeth  move  an  equal 


149 

distance  in  the  same  direction.  If,  however,  these  teeth  move 
unequally,  or  in  opposite  directions,  both  abutments  will  be 
strained  to  the  same  extent.  If  the  molar  is  firm  and  the 
bicuspid  is  loose,  the  greater  strain  will  be  exerted  upon  the 
inlay  in  the  firm  tooth. 

A  loose  tooth  in  moving,  describes  the  arc  of  a  circle  whose 
center  lies  at  the  apex  of  the  root.  The  crown,  therefore, 
changes  its  angle  and  is  displaced  vertically  and  horizontally 
(0,  a,  h,  Fig.  120). 

Whenever  the  loose  tooth  changes  its  angle  bucco-lingually 
in  relation  to  the  firm  tooth,  a  torsional  strain  is  exerted  upon 


Fis.   120. 


Fig.   121. 


Fig.   122. 


the  connecting  bar.  The  torsional  force  exerted  upon  the 
inlay  is  proportional  to  the  angle  of  torsion  (the  movement 
of  the  loose  tooth).  It  is,  however,  independent  of  the  length 
of  the  bar.  The  effect  of  this  force  is  to  twist  the  inlay  out 
of  the  shallow  cavity  upon  the  occlusal  surface  of  the  tooth 
(Fig.  121).  The  point  a  acts  as  a  fulcrum.  To  counteract  this 
force,  a  proximal  cavity  should  be  excavated  with  walls  parallel 
to  the  long  axis  of  the  tooth  {a  and  h,  Fig.  122).  This  locks  the 
inlay  so  that  it  cannot  be  dislocated  by  torsional  strain. 

The  vertical  displacement  is  slight  {a,  Fig.  120),  as  the 
tooth  moves  through  but  a  small  arc  of  a  circle.  The  effect 
of  this  movement  upon  the  inlay  abutment,  will  be  more  fully 
described  later. 

The  horizontal  or  lateral  displacement  [h,  Fig.  120)  of  the 
loose  tooth   exerts   a  strain  upon  the  inlay  abutment  pro- 


150 

portional  to  the  length  of  the  connecting  bar,  and  to  the 
force  apphed  to  the  loose  tooth.  The  lingual  or  buccal  edge 
of  the  inlay  acts  as  the  fulcrum  {a,  Fig.  123).  If  the  inlay  is 
firmly  anchored,  there  is  a  tendency  to  rotate  the  firm  tooth. 
The  mechanical  action  represents  a  lever  of  the  first  class, 
applied  at  right-angles  to  the  long  axis  of  the  tooth. 


Eiff.   123. 


Fie.   124. 


The  mechanical  principles  upon  which  the  anchorage  of 
inlay  abutments  depend  can  most  clearly  and  easily  be  ex- 
plained by  representing  the  tooth  as  a  nut,  and  the  inlay 
and  connecting  bar  as  the  head  and  handle  of  a  wrench. 

If  the  wrench  shown  in  Fig.  126  has  sufficiently  wide  jaws, 
it  v/ill  grasp  a  nut  firmly  when  placed  at  right-angles  to  the 


Fig.    125. 

nut,  as  in  Fig.  125.  Applied  to  the  abutment  in  question, 
this  means,  that  if  the  inlay  were  extended  across  the  occlusal 
surface  and  then  at  right-angles  upon  the  distal  surface  of 
the  tooth,  the  leverage  exerted  by  the  bucco-lingual  movement 
of  the  loose  tooth  could  not  endanger  the  anchorage  of  the 
abutment  (Fig.  124). 

The  best  shape  of  inlay  abutment  for  resisting  the  torsional 
strain  and  the  force  of  the  leverage  produced  by  the  lateral 


151 

movement  of  the  loose  tooth  is  one,  which  in  the  form  of 
the  wrench  Fig.  126,  extends  over  the  mesial,  occlusal,  and 
distal  surfaces  of  the  tooth.  On  one  of  the  proximal  surfaces 
the  margins  a  and  h,  Fig.  122,  should  be  parallel.    Special  care 


Fig.   126.  Fio;.   127. 


must  be  taken  to  make  the  surfaces  a  and  h.  Fig.  136,  represent- 
ing the  jaws  of  the  wrench,  parallel  to  one  another. 

Without  going  into  detail,  the  action  of  a  few  types  of 


Fig.   128.  Fig.   129. 

bridge  abutments  in  resisting  lateral  displacement  of  the  other 
end  of  the  bridge,  may  be  mentioned.  No  special  comment  on 
the  action  of  the  square  post,  is  necessary  in  this  connection. 


Fig.   130. 

The  wrench  Fig.  126  applied  parallel  to  the  nut,  illustrates 
the  principle  upon  which  the  Carmichael  abutment  depends 
in  resisting  lateral  displacement  of  the  other  end  of  the  bridge 
(Fig.  127).  The  wrench  Fig.  128  shows  the  principle  involved 
in  the  use  of  shell-crowns  and  banded  pivot-teeth  (Fig.  129). 
Even  the  alligator  wrench  (Fig.  130)  may  represent  the  proto- 


152 

type  of  a  serviceable  inlay  abutment,  if  the  latter  is  con- 
structed with  a  strong  post  (Fig.  131),  and  provided  with  a 
hook-anchorage  (p.  30). 

Mesio-distal  Movement  of  the  Anchor  Teeth. 

In  this  direction  also,  a  tooth  moves  in  an  arc  of  a  circle 
whose  center  is  situated  at  the  apex  of  the  root.  The  slight 
variation  occuring  in  the  molars  may  be  disregarded.  The 
diagram  Fig.  132  shows  two  pointed  blocks  representing  a 


Fig.   132.  Fig.   133. 

bicuspid  and  a  molar  across  which  a  bar  has  been  laid.  In 
moving,  the  blocks  describe  circles  about  their  pointed  ends. 
If  the  bar  is  moved  distally,  both  teeth,  tipping  in  this  direction, 
support  the  bar  only  on  their  mesial  edges  (Fig.  133).  When 
moved  in  the  contrary  direction,  the  bar  bears  only  upon  the 
distal  edges  of  the  teeth  (Fig.  134).  If  instead  of  a  bar,  a  double- 


Fig.  134.  Fig.  135. 

ended  wrench  with  long  jaws,  is  placed  upon  the  blocks,  no 
tipping  movement  can  take  place,  as  the  blocks  are  firmly  held 
at  right-angles  to  the  long  axis  of  the  wrench,  or,  as  the  blocks 
are  at  right-angles  to  the  wrench,  they  are  held  by  bearing 
surfaces  parallel  to  their  long  axes  (Fig.  135). 

Applied  to  the  inlay  abutment,  these  facts  prove,  that 
movement  of  the  anchor  teeth  in  a  mesio-distal  direction  may 
be  prevented  by  constructing  at  least  two  broad  bearing  sur- 


153 

faces  at  right  angles  to  the  direction  of  movement.  These, 
if  the  tooth  stands  in  its  normal  position,  will  be  parallel  to 
the  long  axis  of  the  tooth,  that  is,  parallel  to  the  direction 
in  which  the  ordinary  complicated  inlay  may  be  removed  from 
the  cavity.  As  this  subject  has  been  fully  discussed  in  Chap.  IV, 
it  need  not  be  repeated  here.  A  very  satisfactory  way  of  in- 
creasing the  area  of  the  bearing  surfaces,  is  to  flatten  the 


Fig.   136. 


proximal  surfaces  of  the  tooth  with  a  diamond  disk  (Plate  V). 
Though  these  two  surfaces  {a  and  b,  Fig.  136)  ought  to  be 
parallel,  it  is  not  possible  to  make  them  so  absolutely.  They 
must  converge  slightly  in  order  to  prevent  distortion  of  the 
impression  during  removal.    A  vertical  section  through  a  Car- 


Fig.  138. 


Fio;.    139. 


michael  inlay  (Fig.  137)  shows  the  application  of  the  wrench 
principle  for  the  prevention  of  mesio-distal  movement. 

When  only  one  anchor  tooth  is  loose,  the  conditions  are 
somewhat  different.  If  oblique  pressure  is  exerted  upon  the 
loose  bicuspid,  the  tendency  is  to  raise  the  inlay  almost  verti- 
cally out  of  the  cavity  of  the  m.olar  (Fig.  138).  The  strain 
upon  the  inlay  is  proportional  to  the  force  exerted  upon  the 
bicuspid  and  to  the  amplitude  of  its  movement.  To  prevent 
a  dislocation  of  the  distal  end  of  the  bridge,  a  very  broad 
bearing  surface  on  the  mesial  surface  of  the  molar  is  necessary 
(Fig.  139).    Such  a  surface  offers  more  resistance  than  a  post; 


154 

though  the  latter  may  also  be  used  to  give  additional  strength. 
If  the  bicuspid  is  firm  and  the  molar  loose,  the  bearing  surface 
should  be  situated  on  the  distal  surface  of  the  bicuspid.  In 
other  words,  whenever  one  end  of  a  bridge  is  in  danger  of 
being  raised  by  the  movement  of  the  other  anchor  tooth, 
a  broad  bearing  surface  should  be  constructed  apon  that 
proximal  surface  of  the  firm  tooth  which  faces  toward  the 


Fig.   140. 

loose  tooth.  As  a  surface  of  this  kind  was.  recommended  to 
counteract  the  effects  of  torsion  (Figs.  121  and  122),  it  becomes 
evident  that  the  broad  proximal  bearing  surface  fulfills  a 
double  purpose.  Special  attention  should  be  paid  to  the  effects 
of  the  movement  of  the  anchor  tooth  just  described,  in  con- 
structing the  posterior  abutment  of  a  bridge  involving  the 


Fig.   141.  Fig.   142. 

anterior  teeth.  Owing  to  the  curve  of  the  dental  arch,  a  linguo- 
labial  movement  of  an  incisor  will  produce  a  vertical  move- 
ment of  an  abutment  situated  in  the  cuspid  or  in  a  bicuspid 
(see  p.  161). 

The  effect  of  an  inclined  position  of  one  or  both  anchor 
teeth  on  the  inlay  abutment  must  also  be  taken  into  con- 
sideration. This  condition  is  most  commomy  met  with  in 
lower  second  and  third  molars  (Fig.  140).  If  vertical  pressure 
is  exerted  upon  a  bridge  supported  by  a  tooth  of  this  kind 
(Fig.  141),  the  latter  is  tipped  still  m^re.  The  bar  rests  on 
the    distal   margin    of   the   tooth,    while   the   mesial   margin 


155 

draws  away  from  the  bar.  The  remedy  in  this  case  also,  is 
a  broad  bearing  surface  (Fig.  142)  against  which  the  incUned 
tooth  can  find  support.  Such  a  surface  is  always  preferable 
to  a  post.  The  latter  may,  however,  also  be  used,  and  in  effect, 
replace  the  second  jaw  of  the  wrench.  Not  only  in  this  abut- 
ment, but  also  in  others,  may  one  of  the  jaws  of  the  wrench 
be  represented  by  a  post  (Fig.  131)  or  an  extension  into  the 
pulp-chamber.  But  whenever  possible,  two  flat  surfaces  of 
sufficient  area  should  be  used.  In  pulpless  teeth  with  crowns 
weakened  by  decay,  this  is  not  always  practicable,  posts  must 
therefore  often  be  relied  upon. 

Vertical  Movement  of  the  Anchor  Teeth. 

Though  even  the  normal  tooth  has  a  slight  movement  in 
this  direction,  it  is  only  in  the  advanced  stages  of  alveolar  ab- 
sorption that  the  movement  becomes  very  noticeable.  If  both 
abutment  teeth  move  the  same  distance,  the  anchorage  of 
the  bridge  is  not  endangered.  When  but  one  tooth  is  loose, 
the  strain  upon  the  firm  tooth  becomes  enormous.  If  the 
abutment  is  strong  enough  to  transmit  the  strain,  the  firm 


Fio-.   143. 


Fie.  144. 


tooth  will  sooner  or  later  loosen  to  such  an  extent  that  failure 
of  the  whole  bridge  becomes  inevitable. 

The  diagram  (Fig.  143)  shows,  that  when  pressure  is  exerted 
upon  the  bar  over  the  loose  tooth,  spaces  are  form.ed  between 
the  distal  margins  of  both  teeth  and  the  bar.  As,  however, 
a  loose  tooth  is  easily  tipped,  it  will  remain  at  right-angles 
to  the  bar,  and  the  effect  of  the  action  will  be  that  of  a  powerful 
lever  of  the  first  class,  the  mesial  margin  of  the  firm  tooth 
acting  as  the  fulcrum  (Fig.  144).  Applying  the  wrench  prin- 
ciple to  counteract  this  force,  large  bearing  surfaces,  mesially 


156 

and  distally,  as  well  as  a  strong  post,  should  be  used  ^Fig.  145). 
If  the  crown  of  the  firm  tooth  is  extensively  decayed,  an  inlay 
abutment  is  contraindicated.  A  strong  shell-crown  should  be 
used  in  its  place. 


Fig.   145. 


Whenever  an  anchor  tooth  is  loose,  the  inlay  abutment 
must  cover  the  whole  occlusal  surface.  It  has  been  shown 
(Chap.  IV  and  Fig.  53),  that  the  anchorage  of  a  self-retentive 
inlay  is  weakest  in  the  direction  opposite  to  that  in  which 


146. 


the  inlay  was  inserted  into  the  cavity.  If  therefore,  the  inlay 
is  firmly  held  in  position  by  the  bridge,  and  the  force  of 
mastication  accidentally  exerted  only  upon  an  exposed  cusp 
of  the  loose  tooth,  the  latter  will  be  pressed  into  its  socket 


Fig.   147. 


and  the  inlay  forced  out  of  the  cavity  in  the  direction  of  its 
least  resistance.  Such  conditions,  necessary  for  the  vertical 
dislocation  of  a  properly  constructed  inlay  abutment,  are  always 
present  when  the  bridge  is  supported  by  more  than  two  anchor 
teeth,  unless,  and  this  is  rarely  the  case,  all  the  teeth  are  of 
exactly  the  same  degree  of  firmness.    Figs.  146  and  147  show 


157 

how  either  the  middle  or  an  end  abutment  tooth  may  be 
depressed.  If  the  inlay  is  to  be  attached  to  the  bar,  it  must 
cover  the  whole  occlusal  surface,  so  that  in  mastication  no 
force  can  be  exerted  directly  upon  this  surface  of  the  loose 
tooth.  The  cusps  should  be  bevelled  v/ith  a  diamond  disk 
as  shown  in  Plate  VI. 

The  Flexible  Abutment. 

As  a  rule,  the  writer,  in  cases  as  those  just  described, 
prefers  to  use  a  loose  or  flexible  abutment;  that  is,  an  inlay 
of  special  form  upon  which  the  bar  simply  rests,  the  bridge 
being  otherwise  supported  by  one  or  more  rigid  abutments. 


Fig.   148. 


If  the  bicuspid  in  Fig.  148  possesses  vertical  movement, 
a  cavity  is  excavated  extending  across  the  middle  of  the 
occlusal  surface  and  involving  the  proximal  surfaces  to  below 
the  contact  points.    The  finished  abutments  in  the  cuspid  and 


Fio-.   149. 


in  the  molar  are  then  connected  with  a  square  platinum- 
iridium  bar  of  sufficient  strength,  which  extends  through  the 
excavated  occlusal  cavity  of  the  bicuspid  (Fig.  149).  With  the 
bar  in  position  a  wax  impression  is  taken.  The  inlay  is  cast  and 
set  into  place.   The  bridge  is  then  finished  in  the  usual  manner. 


158 

by  casting  occlusal  surfaces,  with  or  without  removable  por- 
celain facings,  onto  the  bar.  When  the  bridge  has  been  set, 
the  bicuspid  is  free  to  move  in  a  vertical  direction.  Mesio- 
distal  movement  is  prevented  by  the  adjoining  teeth  of  the 
bridge  (Fig.  150),  while  the  flat  surfaces  of  the  bar  prevent 
bucco-lingual  motion  (Fig.  149). 


Fig.   150. 

When  the  conditions  are  similar  to  those  shown  in  Fig.  147, 
it  is  not  advisable  to  let  the  bar  rest  merely  on  the  occlusal 
surface  (Fig.  154).  Especially  is  this  true,  when  the  tooth 
adjoining  that  of  the  abutment  is  also  loose.  In  this  case, 
the  end  of  the  bar  must  be  bent,  or  a  piece  soldered  on,  at 
right-angles,  and  be  extended  well  toward  the  cervical  margin. 


Fie.   151. 


The  inlay  is  constructed  as  described  above,  and  set  before 
the  introduction  of  the  bridge  (Fig.  151). 

The  flexible  abutment  may  also  be  used  to  advantage  in 
connection  with  firm  teeth.  Such  bridges  v/ith  but  one  rigid 
abutment,  though  not  often  met  with  in  practice,  are  by  no 
means  new.*)     Owing  to  its  many  advantages,  especially  in 

*)  W.  S.  Davenport.  Dental  Bridge  and  Pier  Construction.  Trans.  N.  Y. 
Institue  of  Stoma;tology,   1902. 


15!) 


connection  with  inlay  work,  this  type  of  bridge  deserves  full 
recognition  by  the  profession  at  large. 

The  most  common  form  of  flexible  abutment  is  the  lug 
(Fig.  152).   Its  bearing  surface  is,  however,  too  small,  and  there 


3' 


M 


Fig.   152. 


Fig.   153. 


is  the  constant  danger  of  the  abutment  tooth  moving  away 
and  leaving  that  end  of  the  bridge  entirely  unsupported. 

The  abutment  shown  in  Fig.  153,  a  variety  of  socket  joint, 
at  one  time  used  by  the  writer,  is  open  to  the  same  objection. 
Beside  this,  strong  distal  movement  (tipping)  of  the  molar 
invariably  forced  out  the  inlay  in  a  vertical  direction,  after 
a  longer  or  shorter  time.  Only  where  the  length  of  the  bar 
was  equal  to  the  width  of  one  bicuspid,  and  both  anchor 
teeth  were  perfectly  firm,  has  this  form  of  abutment  been 
successful  in  practice. 

If  both,  the  tooth  adjoining  the  abutment  and  the  tooth 
supporting  the  other  end  of  the  bridge,  are  firm,  the  flexible 


Fig.   154. 

abutment  shown  in  Fig.  154  may  safely  be  depended  upon. 
(Section  same  as  Fig.  149.)  The  cavity  is  easier  to  prepare 
than  that  of  Fig.  151,  as  but  one  proximal  surface  is  involved. 
The  construction  of  the  inlay  is  also  less  difficult,  especially 
about  the  end  of  the  bar,  as  this  is  here  situated  upon  the 
easily  accessible  occlusal  surface. 


160 

Though  possessed  by  all  flexible  abutments  more  or  less, 
the  advantages  enumerated  below  refer  particularly  to  the 
forms  shown  in  Figs.  150,  151  and  154. 

The  flexible  abutment  interferes  but  very  slightly  with  the 
physiological  movement,  while  at  the  same  time  preventing 
any  abnormal  motion  of  the  anchor  tooth.  The  lateral  move- 
ments of  the  tooth  (Fig.  150)  are  in  direct  ratio  to  those  of 
the  end  abutment  teeth.  If  these  are  firm,  the  loose  tooth 
cannot  move  beyond  physiological  limits.  (Compare  Fig.  148 
and  149.) 

When  the  flexible  abutment  is  situated  at  the  end  of  a 
bridge  with  but  two  piers,  lateral  displacement  is  dependent 
upon  the  firmness  of  the  other  anchor  tooth  and  upon  the 
length  of  the  bar.  With  a  long  bar  a  perfectly  firm  tooth, 
owing  to  a  slight  rotary  motion  in  its  alveolus,  will  permit 
the  loose  tooth  to  move  laterally  somewhat  more  than  normal. 
The  same  is  true,  however,  of  every  bridge,  even  with  rigid 
abutments. 

Mesio-distal  movement  can  occur  only  within  physiological 
limits,  and  in  a  normal  manner.  The  distance  is  determined 
by  the  movement  of  the  firm  anchor  teeth  (Figs.  148  and  150), 
or  by  the  firm  adjoining  tooth  (Fig.  154).  The  anchor  tooth 
carrying  the  flexible  abutment,  not  being  attached  to  the  bar, 
does  not  follow  the  movements  of  the  bridge  bodily,  but  moves 
in  the  arc  of  a  circle  (Fig.  120). 

Vertical  movement  is  in  no  way  interfered  with.  This  is 
one  of  the  most  important  advantages  of  this  type  of  bridge. 
When  there  are  but  two  abutments,  each  tooth  moving  in- 
dependently, can  assume  a  position  in  which  all  points  of  the 
root  bear  equally  against  the  walls  of  the  alveolus  when  force 
is  exerted  upon  any  point  of  the  bridge.  The  peridental 
membrane  will  remain  healthy,  and  no  inflammatory  changes 
in  the  bone,  due  to  localized  pressure,  will  take  place. 

Another  advantage  of  the  flexible  abutment  is,  that  in- 
clined anchor  teeth  do  not  cause  serious  difficulties  in  the 
construction  of  the  bridge  (Fig.  155).  Each  abutment  being 
made  seperately,  can  readily  be  brought  into  place.  If  two 
inlay  abutments  are  used,  each  one  while  being  set,  can  be 


Ifjl 

adapted  perfectly  to  the  margins  of  the  cavity;  a  feat  difficult 
to  accomplish  with  rigid  abutments  in  the  form  of  inlays. 
In  determining  the  force  exerted  upon  an  inlay  abutment, 
another  factor  beside  the  movement  of  the  teeth  must  be 
considered,  that  is,  the  width  of  the  masticating  surface  of 
the  bridge  suspended  between  the  abutments.  If  this  surface 
is  too  wide,  pressure  exerted  at  but  one  point  near  the  edge 
{a,  Fig.  150)  will  set  up  a  severe  torsional  strain  in  the  bar, 
which  in  turn  transmits  it  to  the  inlay.  Such  surfaces  should 
therefore  be  niade  slightly  narrower  than  normal,  especially 
near  the  flexible  abutment.  Attention  should  also  be  paid, 
that  the  bar  or  central  line  of  occlusion  divides  this  surface 
equally,  as  pressure  exerted  on  the  entire  masticating  surface 


Fig.    155. 

of  the  bridge  will  then  produce  no  torsional  strain.    With  un- 
equally divided  surfaces,  this  is,  however,  not  the  case. 

In  discussing  the  effects  of  strain  upon  inlay  abutments, 
only  those  in  the  molars  and  bicuspids  have  been  considered. 
All  that  has  been  said,  applies  also  to  abutments  in  the  anterior 
teeth.  Another  factor,  however,  plays  an  important  part.  The 
bicuspids  and  molars  are  situated  in  a  straight  line,  while  the 
anterior  teeth  occupy  a  position  on  the  arc  of  a  circle.  This 
difference  in  alinement  produces  a  difference  in  the  distribu- 
tion, magnitude,  and  direction  of  the  strain  exerted  on  the 
abutments  and  on  the  bridge.  To  describe  the  difference  of 
effects  in  detail,  would  neccessitate  the  repetition  of  much  that 
has  already  been  explained.  By  following  the  description  of 
the  strain  exerted  upon  the  molars  and  bicuspids,  anyone 
who  is  sufficiently  interested  can  for  himself  determine  the 
effects  on  the  anterior  teeth.  The  task  becomes  very  simple 
if  a  wire,  the  length  of  the  bridge,  is  bent  in  conformity  to 

Bcidecker,  Metallk;  Inlay.  11 


162 

that  part  of  the  dental  arch  in  which  the  bridge  is  situated. 
By  moving  one  end  or  the  middle  of  the  wire,  reproducing 
the  movements  of  the  abutment  teeth,  the  effects  upon  all 
parts  of  the  bridge  can  readily  be  determined. 

To  specify  the  exact  conditions  in  which  inlay  abutments 
are  indicated,  is  not  possible.  A  rigid  inlay  abutment  may 
safely  be  used  when  the  space  to  be  bridged  does  not  exceed 
the  width  of  two  bicuspids,  and  when  the  anchor  tooth  is 
firm  and  possesses  a  strong  crown.  The  use  of  the  flexible 
inlay  abutment  is  not  so  limited,  especially  when  there  are 
more  than  two  anchor  teeth.  In  some  favorable  cases  of  this 
kind,  one  rigid  and  two  flexible  abutments  may  be  used,  as 
in  Fig.  148  when  the  bicuspid  as  well  as  the  other  anchor  teeth 
are  firm. 

It  is  not  the  intention  of  the  writer  to  make  a  plea  for  the 
extensive  use  of  the  inlay  abutment.  But  there  are  cases  where 
it  undoubtedly  offers  an  ideal  form  of  anchorage.  When  a 
space  between  two  healthy,  reasonably  firm  teeth  is  to  be 
bridged,  say  a  space  due  to  the  premature  loss  of  the  first 
molar,  an  inlay  bridge,  constructed  as  follows,  is  to  be  pre- 
ferred to  any  other  form  of  bridge-work.  In  such  cases  the 
writer  would  recommend  a  rigid  inlay  abutment  in  the  second 
molar,  and  a  flexible  abutment  in  the  second  bicuspid.  The 
pulps  in  both  teeth  being  intact,  they  should  in  no  way  be 
interfered  with.  Recurring  to  the  principle  of  the  wrench, 
the  construction  of  large  bearing  surfaces  upon  the  mesial 
and  distal  surfaces  of  the  molar,  parallel  to  the  long  axis  of 
the  tooth,  becomes  necessary.  The  quickest  and  most  pain- 
less way  of  preparing  these  surfaces  is  to  flatten  the  tooth 
with  a  diamond  disk  (Fig.  136,  or  as  shown  in  Plate  V).  One 
or  both  proximal  cavities  should  be  deepened  slightly  (some- 
what less  than  shown  in  Plate  V)  in  order  that  the  inlay  may 
resist  torsional  strain.  The  occlusal  surface  is  cut  out  to  a 
sufficient  depth  with  a  knife -edged  stone,  so  that  the  platinum- 
iridium  bar  does  not  interfere  with  the  bite,  and  lies  well 
within  that  part  of  the  inlay  which  fills  this  cavity  (Fig.  156). 

The  flexible  abutment  is  constructed  either  as  in  Fig.  151 
or  in  Fig.  154.    If  both  the  bicuspid  and  molar  are  firm,  the 


163 

latter  method  is  used,  if  the  bicuspid  is  somewhat  loose  the 
former  should  be  employed.  The  platinum-iridium  bar,  re- 
presenting the  frame-work  of  the  bridge,  should  bear  upon 
each  abutment  so,  that  any  force  exerted  upon  it  vertically, 
is  transmitted  equally  to  the  lingual  and  buccal  halves  of  the 
anchor  teeth.  The  bar  should  be  square  and  be  about  2  mm. 
(i/ie  inch)  in  thickness.  One  end  of  the  bar  is  bent  so,  that  when 
laid  upon  the  occlusal  surfaces  of  the  abutment  teeth,  the 
bent  end  extends  into  the  distal  cavity  of  the  molar  parallel 
to  the  axial  wall  and  almost  to  the  cervical  margin  (Fig.  156). 
Inlay  wax  is  introduced  into  the  cavity  and  roughly  modelled. 
The  bar,  previously  roughened,  is  then  warmed  and  forced 


Fig.   156. 


into  place,  the  impression  finished,  and  the  inlay  cast  onto 
the  bar  in  the  usual  manner.  In  difficult  cases  an  indirect 
impression  is  taken  or  a  stone  model  made,  and  the  wax 
model  again  tried  in  the  mouth.  In  order  that  the  alinement 
of  the  other  end  of  the  bar  may  be  correct  while  taking  the 
impression  of  the  molar  cavity,  the  writer  excavates  the 
occlusal  surface  of  the  bicuspid  only  so  deep,  that  the  bar 
rests  in  the  position  that  it  is  to  occupy  later.  After  the  rigid 
abutment  has  been  cast,  the  cavity  of  the  bicuspid  is  com- 
pletely excavated,  an  impression  taken  with  the  bar  in  place, 
and  the  inlay  cast.  The  margins  of  both  inlays  are  there- 
upon burnished,  and  the  one  in  the  bicuspid  set  into  the 
cavity.  At  this  stage  the  bridge  consists  of  two  perfectly 
fitting  inlays,  the  one  rigidly  and  the  other  loosely  connected 
with  the  bar.  Upon  the  latter  a  tooth  is  modelled  in  wax, 
and  then  cast.  If  desirable  a  removable  porcelain  facing  can 
be  used. 

11* 


164 

In  conclusion  the  writer  wishes  to  emphasize,  that  the  inlay- 
abutment  is  not  applicable  to  every  case,  but  that  whenever 
it  is  used,  it  should  be  properly  constructed  with  due  regard 
to  the  strain  which  will  be  put  upon  it.  In  determining  the 
proper  form,  it  is  always  advisable  to  regard  the  inlay  abut- 
ment as  a  combination  of  two  wrenches,  the  one  acting  parallel 
to  the  long  axis  of  the  tooth  to  prevent  tipping,  the  other 
at  right-angles  to  the  first ,  to  prevent  rotation  and  lateral 
movement. 

It  is  a  regrettable  fact,  that  in  the  construction  of  dental 
bridge-work  but  little  thought  is  given  to  the  distribution  of 
force  within  the  structure.  The  dentist  should  follow  the 
example  of  the  engineer,  who  calculates  the  stress  and  strain 
of  every  part  of  a  bridge  before  begining  with  its  construction. 


Index. 


AVjutment  teeth 

inclined   154. 

movement  138,   152,   155. 
Adaptation  at  margin  5,  10,  12,  135. 
Adhesion  of  cement   17,   142. 
Advantages  of  metallic  inlays   13. 
Amalgam  model  92. 
Ames  W.   V.   B.   143. 
Anchorage 

by   combining   two    cavities    32,   81, 
88,  89. 

dove-tail  31,  78,  80. 

fissure  29,  46,   76. 

groove  29,  44,  85. 

hook  30,  82,   152. 

pin  33. 

reciprocal  32. 
ApjDaratus  for  casting 

Biber  122. 

Elgin   126. 

Jameson   123. 

Solbrig  121. 

Taggart  119. 
Artificial  stone   111. 
ArvineF.  B.  112. 

B 

Bearing  surfaces  154,   154. 
Bevelling 

occlusal  surface  27,  49,   77. 

enamel  margin   63,   66. 
Bite 

for  models  92. 

on  inlay   136,   146. 

on  wax  form  97,   98. 
Black  G.  V.   53,  58,  65. 
Blowholes  116,   136. 
Bodecker  C.  F.  W.  8. 
Bonwill  mallet  24,   138. 
Box-shape  36,  55. 

cavity,  simple  37,   38. 

cavity,  complex  42,   56. 

extreme  57. 

inlay  42. 


Bridge  abutments    148. 

bar   159,   162. 

Carmichael   151,   153. 

flexible   157. 

indications   162. 

lug   159. 

socket  159. 

wrench  principle   150,    152,    164. 
Bubbles 

in  investment  109. 

on  inlay  132. 
Burs  68,  146. 

C 

Carborundum 

floixr   147. 

stones  68. 
Caries 

point  of  origin  53,   59. 

progress  54. 
Carmichael  inlay  abutment  151,  153. 
Casting  metals  112. 

shrinkage  113,  ll5. 
Cavity  preparation  74. 

box-shaped  36,  38,  57. 

saucer-shaped  35. 
Cement 

adhesion  17,   142. 

anchoring  the  inlay   17. 

compression  strength  21,  41. 

disintegration  7. 

hollow  inlays  52,   103. 

hydraulic   140. 

reaction  of  dentine  8. 

solubility  140. 

tables   140,   141. 

tensile  strength  24,   36,   52. 

thickness  of  layer  40,   139,   140. 
Coefficient  of  contraction 

base  metals  113. 

noble  metals   113. 
Combination  inlays  88,    127. 
Compression  strength  21,  41. 
Contact  point 
form  61. 


166 


on  inlay   131. 

on  wax  model  100. 

in  direct  impression  99. 

in  indirect  impression   92. 

position  27,  61. 
Contour 

of  tooth   59. 

of  filling  60. 

of  wax  model  99. 
Copper  rings  90. 


D 


Davenport  W.   S.   158. 
Defective  inlays  132. 
Dentin 

drying   143. 

reaction  8. 
Diamond  disk  60,  80,  81,   162. 
Disadvantages  of  metallic  inlays  6, 12. 
Disinfection  of  cavity   143. 
Direct  impression  92. 

instruments  95. 

method  96. 

wax  for  93. 
Dove-tail  anchorage  31,  78,  80. 
Drying  the  cavity  143. 

E 

Enamel  margin  62. 

bevelhng  63,  66. 
Enamel  prisms  62. 

cleavage  62,  65. 

course  64. 
Engraving  instrument  25,   137. 
Extension  for  prevention  58. 


F 


Flexible  inlay  abutment   157. 

Finishers  146. 

Finishing  145. 

Fissure  caries  54. 

Fissure  anchorage  29,  46,  76. 

advantages  45. 

excavation  for  54. 
Frink  C.  H.   126. 

a 

Gas  pressure  119. 
Gold  24  kar.   12,   117. 
22  kar.   12,   117. 
coefficient  of  contraction  113. 
Goldfillings  55,  58,  60. 
Granular  surface  of  inlay  133. 


Grinding  instruments 

of  aluminum  70. 

of  copper   70. 
Groove  anchorage   29,  44,  85. 
Guttmann  pincette  145. 


II 

Head  J.   11,   139. 
Herbst  inlay  104. 
Hersey  G.   S.   24. 
Hinman  inlay  106. 
Hollow  inlays  2,  52,   106. 
Hollo"w  wax  models  102. 
Hook  anchorage  30,  82,   152. 


Impression 

direct  92. 

indirect  90. 
Impression  material  90. 
Indications  for  metallic  inlays   14. 
Indications  for  inlay  abutments  162. 
Inlay  abutments  148. 
Inlays 

bite  136,  146. 

blowholes  116,   136. 

casting  107. 

combination  127. 

defective  132. 

evolution  1. 

finishing  145. 

fitting  131. 

gold  24  kar.   12,   117. 

gold  22  kar.   12,   117. 

granular  surface    133. 

Herbst  104. 

Hinmann  106. 

hollow  2,  52,   106. 

polishing  147. 

roughening   17,  24,  49,  51,   137. 

rounded  edges   135. 

setting    144. 

silver  118. 

sponge  gold  105. 

swedged  105. 

undercutting  18,  22,  39,  49,  51,  137. 
Instrximents 

for  modelling  wax  model  95. 
Interproximal  space  61,  99. 
Investing  material  107. 

artificial  stone  111. 

bubbles  109. 

composition.  112. 

expansion   110. 


I 


167 


Jameson  machine   123. 


Lane  114. 

Leverage  oni  nlay  abutment  150,  155. 

M 

Mastication,  cleansing  action  of  58. 
Metal  for  casting  112. 

coefficient  of  contraction   113. 

overheating  116,   132. 

unclerheating   135. 
Miller  W.   D.    11. 
Model 

amalgam  92. 

bite  for  92. 

cement  91. 

Melott's  metal  92. 

plaster  91. 

Spence  metal  92. 
Mold  107,   110. 

drying  110. 

heating  111. 
Movement  of  abutment  teeth 

biicco-lingual   148. 

mesio-distal   152. 

physiological   149. 

vertical   155. 
Mucin   11. 

0 

Oxygen  apparatus   124. 


Parallel  walls  37,  40,  43,  46. 
Parallel  surfaces  on  inlay  42. 
Pin  anchorage  33. 
Plaster  model  91. 
Polishing   147. 

Porcelain  5,  7,  23,  28,  88,   127. 
Poundstone  G.  C.   140. 
Pressure  in  casting  3,   118. 

centrifugal  123. 

direct  contact    122. 

gas   119. 

steam  121. 

vacuum  126. 
Pressure 

contraction  of  metal  under  113. 
Pressure  on  inlay  28,  36,  46. 

obhque  29,  46. 

vertical   28,   36. 
Price   W.    A.     109,    111,    113,    115, 
120,   124. 


Projections  on  inlay   132. 
Protection  for  handpiece  72. 
Pulp,  danger  of  injxiring  55,   76. 

R 

Retention  16,  26,  35. 

cement-retention  17. 

self-retention  26. 
Right-angle  handpiece  71. 
Roach's  wax  carver  102. 
Roughening   the   inlay    17,    24,    49, 

51,    137. 
Rounded  edges  135. 

S 

Sachs  W.    112. 
Saucer-shaped  cavities  35. 
Seam   10. 

dissolution  of  cement   10,   11. 

metallic  inlays  6,   12. 

porcelain  inlays  5. 
Secondary  caries  9. 
Self-retention  26. 
Silver   118. 

Solbrig  O.   3,   122,   123. 
Solbrig  pliers  121. 
Spence  metal  92. 
Sponge  gold  inlay   105. 
Steplike    cavity  preparation  44,  55, 

57,  84. 
Stones  68. 

mounting  68. 

truing  69. 
Suction  wax  carver   102. 
Swedged  inlays   105. 

hollow  2,   106. 
Swedging  apparatus  106. 

T 

Tables 

coefficient  of  contraction  of 
metals   113. 

properties  of  cement   140,   141. 
Taggart  W.  4,    110,   119,  145. 
Taggart  machine  119. 
Tweezers,  Guttmarm.  145. 
Torsion  149. 

U 

Uhlenhuth  109,   113. 
Undercuts 

in   the  inlay    18,    22,    39,   49,    51, 
137. 

in  the  wax  model  99. 

in  the  tooth  22,  49,  50,  51. 


168 


Undercuts 
form  of  22, 
mechanics  of  21. 


Vacunm  casting  machine   126. 
Van  Horn  C.  S.    114. 


W 

Ward  M.  L.   112,   114,   117. 


Wax 

cohesion  94. 

color  95. 

hardness  94. 

instruments  95. 

recovery  94. 

scraping  94. 

suction  carver   102. 
Wax  model 
■     expanding  the   114. 

hollow  102. 

modelling  in  the  mouth  96. 

mounting  upon  the  sprue   100. 
Wrench  princij^le  150,   152,   164. 


li 

mil 

0 

p  I  <i  lit 


RK.549 
Bodecker 

The  me  tall  ic-JinlayL^ 


B6:? 


RK  549  B63  cT'^ libraries fhsis^. 

The  metallic  inlay 


2002376970 


DEC  30  19% 


